If I were you, I would just try to find some way of subtly asking if this is a thing she would like. There’s always the slight possibility that your wife might find the solution of divided plates embarrassing or patronising.
I agree with Mangetout. I love my wife dearly but I would never surprise her with something like this. If and when you find a suitable supplier, show them to her and ask if she would like them. Even better, if it’s possible, take her somewhere to see and handle some. These things are never the same as the pictures if you don’t already know the product.
It’s OK. As strange as it sounds, very few people actually have decent search skills. Everybody knows that Google is right there, and because they use it, they think they have search skills. But they don’t.
On those occasions where I’m helping someone and looking over their shoulder as they search for one thing or another, I’m almost always amazed, and not in a good way, at the search terms they use. Apparently it is an art after all.
I dunno if I was looking for such a thing if I’d have tried “portion plate.” It seems like an odd turn of phrase to me.
Ages ago I’d bought (at Williams Sonoma I think) a stainless steel mesh cylinder for cooking pasta in. It was sized to fit in a stock pot and had a bail on the top so you could lift it out when the pasta was done, a lot easier than dumping a hot, heavy pot through a colander. It was crushed during a move recently and I’d been looking for a replacement. “Pasta strainer” yielding nothing like what I was looking for. Then I tried “pasta basket.” Bingo.
One that I didn’t see mentioned:
Most Indian restaurants serve the meal with each item in individual dishes on a tray. Including things you add to each other in your preferred proportions.
More dishes to wash, but guaranteed not to mix. :smack:
I think it’s nice that you want to get her a special plate. I don’t like my food touching either. I frequently use a fork to add that separation between items and sometimes use a napkin or paper towel to clean up the area of separation.
Just the other day, DH was attempting to add something to my plate that he wanted me to try. I already had my food items placed ‘just so’ and his incoming item was gonna mess with my already established order. I immediately felt anxious about it but managed to stall him long enough to make a proper space for the incoming item. Another time, he handed me a bowl of salad with a piece of warm, grilled fish on top. Yikes! So wrong! It actually gave me a stomach cramp. I had to deconstruct the whole thing. My thoughts about it were that ‘a hot thing doesn’t belong on a cold thing’ and that ‘salad dressing and fish can’t touch.’ I had to remove the ‘damaged’ salad pieces, clean the fish, etc. Yet, oddly, finding a bug in a salad would not bother me. Those things ‘go together.’
I have quite a few food weirdnesses, but I know they are mine and that other people likely don’t even think about things like that. I don’t usually say anything about it or cause any trouble about it, but just fix the ‘problem’. I eat the same 4 items for lunch every day and have done so for years. It just suits me to do so. It’s orderly. Occasionally, I don’t do it. That’s OK, too. Items touching other items won’t ruin my day, but I won’t be happy about it either, so a plate with divisions would be nice to have. I do have a couple of psych diagnoses, if you had not guessed that already. LOL!
If the phobia is really that intense you could always use multiple smaller plates or bowls.
I know people like this, too. I think it’s a visual thing. If you ordered broccoli with a special beef sauce at a restaurant for $15, they would love it, but if the juice from their beef tends to run to the broccoli, it’s a problem. It’s really just a visual thing.
How does she keep the food apart in her stomach?
Rumen, reticulum, omasum, abomasum.
ETA OP, I’m not calling your wife a cow/ruminant. 
Sometimes people overthink these things. I just Googled the exact words you used to describe it – “stainless steel mesh cylinder for cooking pasta in,” but without quotes – and found it right away.
Like others have said you could just get some cafeteria trays likethese. Easy to clean and stack. Also a great way to serve people in bad or even sitting in front of the tv because they keep everything together. Plus only $3.60 each!
Not sure if they fit into a dishwasher.
I don’t mind my food touching, but I don’t like it when the wet part of one food (like pickle juice or meat juices, etc) seeps into other food on a plate. I always use a separate plate for wet foods.
Some people describe divided plates as picnic plates. A lot of depression glass sets included divided plates. Available in may colors.
Thank you all very much, I went with the Corelle white ones and with some of the glass depression dishes.
Ordered and on their way.
I know she will love them. Really appreciate it.
We have a set of these which I think came from a diner. We love that they keep things separated, but it led to the family joke about having to come up with a “third thing” to fill out the plate. 