I knew someone just like this. But she was in her 80s. I assume your girlfriend is not, so I agree with those who think she needs to talk to a doctor.
I used to be real scrawny, ran unusually low blood pressure & had a slow heart rate. I was almost, but not quite, cold-blooded.
Any temp below about 80 was cause for shivering. Air conditioning was the worst; a cold draft blasting through what would otherwise be a nice comfortable 85 degree environment. I needed to eat about 3500 cal/day just to stay alive. Being other than miserably cold was a rare luxury, savored on occasional afternoons in sun-baked closed rooms.
SoCal seems to create people with odd temperature tolerances. I grew up there too. My brother, raised in the exact same environment (duh) was the opposite, comfortable in the 60s & hot when it got to be 72. He was not, however, scrawny or slow-hearted.
When I was in my cold phase I’d sure have jettisoned any room mate who tried to make me live in temps incompatible with a decent life. If you’re not a cold-blooded person you just can’t appreciate what it’s like. For folks from the the cold country, imagine going all winter with your house heated to only 55F, and you can only wear a t-shirt when at home. The cold won’t kill you, but you’ll never be anything but uncomfortable & stiff & almost shivery. That’s how 75 felt to me up through about age 30.
After I gained about 30lb of muscle & 50lb of blubber over that I no longer have the shivering problem. Cold (<70) still sux, but at least now I can cut back to 3000 cals a day & not lose weight.
For the OP: Until she gains 100 lbs you’re not going to get her comfortable below the temps she likes now. And being cold all the time is one miserable existence. My advice is to feed her lots of pasta, adapt to her temperatures, or trade her in on a new GF.
Is she from Eastern Europe?
It seems like her main problem is the AC. I can identify with that. Unless it is well over 100 degrees out, I am never comfortable with the AC on. It’s not just the temperature, it’s the quality and movement of the air. And the disconnection with the outside world- especially the transition between inside and outside. It just doesn’t feel right and I can’t settle down and be comfortable.
I also agree with LSLGuy. Body weight is a major factor. I never figured out how people feel uncomfortable in what I consider mildly cool weather until I realized that these people were all 30-50 pounds heavier than me. Even a little bit of padding is like wearing an extra layer of clothes. Anyway, despite being certified as completely healthy (for my job I’ve had to get every medical test imaginable) I am cold blooded.
Fairly? I don’t know.
There does have to be compromise.
My husband is a big ol’ boy, has always been miserable at high temps, and would like the house about 60 degrees.
I’m scrawny, will usually have on 2 layers of clothes except in High Summer, and would pick 75 degrees as tolerable.
Heat makes him sweaty, cranky, dizzy, and sometimes, downright ill.
Cold make me shiver, ache, grit my teeth, and I just want to hibernate.
However.
We both live here, and plan on continuing for some years.
It’s…about a 66-70 degrees range we work with for the thermostat.
I’ve found it also depends on whether it’s forced air or radiant heat.
If he turns the fan on in his direction, I can deal with a light blanket while watching TV.
If we go out to eat, and the cafe is ByGodFreezeYourAssOffRidiculousCOLD, I just want to get stabbity at everyone in the place. I take a sweater or jacket with me even in the Summer. Crazy people, anyway.
My older sister is a)always cold and b) very sensitive to all sensory imput. I like the temp at 71, she likes it about 78. We keep it around 75. I’m not that uncomfortable, most of the time (for those of you saying “Put on more clothes,” I’m inclined to walk around in my underware) and she’s usually happy in a sweater. Compramise is the name of the game in any relationship.
This. I’m fairly cold-tolerant, but can’t stand a breeze of any sort. Moving air makes me edgy and twitchy, a prolonger exposure downright miserable. A nice nightmare to me would be forced to live on the coast, where it never stops blowing (here at least).
My sister likes to keep the apartment at 75 or so, and her room gets to be almost 80 at times. I like to keep it closer to 70, and my bedroom has the window open, and it stays near 60 in there. We agree that 73 or so isn’t that bad. I can deal being a little warm, or go in my bedroom, and she can get a blanket, or go to her bedroom.
Turn the temperature down until you’re both uncomfortable. Then one of you is not comfortable at the expense of the other, and you save money!
When I come home from work I turn the temp up from 56 to 63. Yes, it’s cold, but I only get naked for showers and activities that will keep me warm anyway.
I don’t like the ac on unless it is baking hot outside, so right now in Houston, when it’s 80 outside, it’s about 80 in the house and I think it’s great. Then my boyfriend comes home and first words out of his mouth “God, it’s fucking HOT in here!” and goes straight to the thermostat and puts in on 66 and THEN I get my hug and how was your day. After that, I walk around with a blanket and hoodie on. Came close to getting a Snuggie until I saw how cheap the material was. So yeah. I don’t have a suggestion. I just deal with it, because I’m less of a bitcher, and it’s easier for me to be cold than for him to be ranting and raving because it’s a little warm.
Except at night, then I like it Arctic.
There would be bloodshed if I turned the temp up that high. I like it warm, he likes it cool. We keep it between 67 and 70 and will each adjust the thermostat when the other isn’t looking. This happens a dozen times a day. He’s out in the garage right now so I’m groovin’ at 70. I’d actually like it at 72, but it’s not financially prudent.
Oh yes, here was the solution I was meaning to say! Just constantly go behind each other’s backs, at some point it gets so absurd it’s hysterical! We messed with it so much the little door that covers the buttons straight up broke off, so now we just break it off, then delicately perch it back on when done.
See? There’s no discussion. No agreement. No *fight! *Our 20 year relationship is based on this tactic. Why discuss it? I will never agree with him that the house is comfortable at 67. Rather than a 5-month-long fight, we agree to disagree and give each other an hour or so on their preferred temp before switching it back.
And regarding the little door, I find it’s easier to change the setting without being noticed if you don’t have the noise from the door giving you away. 
Our A/C is stuck in the wall and uses big knobs, not a thermostat. You turn it on High, Medium, or Low. You set it for a cooling factor of 1-9.
Where we sit at our computers, the a/c is right in front of us. If either adjusts it, the other can clearly see them.
When we sit in the couch watching tv, the a/c is right behind us. It’s eminently obvious when someone changes it.
So, rather than sneaking, we’ll just boldly walk up and change it. That’s when the conversation starts. “Why did you turn the a/c down so the compressor is not on? It’s 81 degrees in here.”
“Because I’m cold.”
“Well 81 isn’t cold, it’s ridiculously hot. I’m already naked, I can’t get more naked.”
or…
“Why did you turn the a/c up so that the compressor is on?”
“Because it’s hot in here.”
“I’m cold.”
“Well I’m hot.”
I think I have the perfect solution.
(Warning: sound!)
Could you arrange your furniture differently? Put your computer on the north wall and hers on the south.
We share a desk, so it’s going to be tough to split us up that far. And the apartment is not exactly spacious. Good idea, though.