This is GQ, so I’ll answer first factually. Eat lots of calories every single day, even when stressed. High calorie food is cheap and easy to find at fast food restaurants and vending machines. Weight gain supplements can be found at drugstores and GNC stores. Her doctor can also provide a list of high calorie foods, and can prescribe supplements if necessary.
Now, as someone who is female, tall, and thin, please let me share my experience.
I am 5’10” and weighed between 100 and 110 pounds until I was 33. When I was a teenager I consulted my family doctor for advice, ate everything in sight, tried nutritional and weight gain supplements, and ate tons of junk food. I have always been fairly active, and though I was thin, I had no trouble competing in 10k races, swimming, or in ballet. I was healthy and strong at that weight, and I never missed a period. I didn’t need to gain weight; I wanted to gain weight in order to stop the constant comments from friends and strangers. Those comments bothered me a lot when I was younger, but with every passing year I cared less about other people’s opinions.
At 37, I weigh 125-130. Still nothing wrong with me, still active, still eating quite a bit more than most people expect. According to the frequency of comments I get from pushy strangers, I’m apparently still too thin. After 25+ years of unsolicited opinions, I still don’t care. Some people are thin, some are thick, some are in between. If we all looked alike, then who would be left to criticize?
If your girlfriend is happy and healthy, there is no need to push her to gain weight, and unless you suspect an illness or eating disorder, there is no reason that she *must * try to gain weight. If she has IBS, then she is already under a doctor’s care, and how much she weighs is no one’s business but her own. Please don’t give her a hard time about being thin. Lots of 17 year olds are thin. She is still growing, and her body is still changing. There are bigger and better things to focus on at that age.
As far as the wrinkles under her eyes, does anyone else in her family have wrinkles around their eyes? Maybe a common trait for her family? If not, does she have allergies and often rub itchy eyes? Lots of moisturizers for the eye area claim to plump up the area under the eye in order to give a smooth appearance. Here is a link to Sephora, and a list of under-eye creams in order of customer rating.