If they were family they would probably share too. If you were co-workers, do you compliment your colleague on their higher salary and things they can afford? I don't.
The first paragraph of your post certainly sounded like she was into looks, that's why I said what I said.
Well if she's not and if she's not the one who brings up the subject, why do you, when it makes you feel down?
Using your metaphor, your behaviour is more like the kid who got 60 on a test complimenting the one who got 90 and then being unhappy that the one that got 90 said they could have done better still.
Just don't bring up the topic if the conversation that follows makes you feel sad.