So, I need some advice about how to handle a friendship. I've known this girl for 4 years (we're classmates) and we really started hanging out the past two years. We both moved to the same city this September which intensified the amount of time we spent together (by which I mean we hung out, like, once a week), but I am under the impression she doesn't have a lot of friends here beyond her university friends (and there are only 4 of us), even though this is her hometown. She is kind and enthusiastic and a has good intentions, however, she gets on my nerves in a way that I haven't experienced since my off-kilter teen years. I pretty much have boundless patience and am pretty good at either ignoring things that sort of irritate me or addressing the issue with a friend. I've tried both with her (the instance where I addressed the issue involved her being gross about other peoples' weight multiple times- she has recently lost a lot of weight- and I called her on it... but she still does it then just apologizes). I think the overarching link between all the little things that set me on edge is that she is very immature for a 21 year old and I just can't connect with that.
I end up being kind of short with her and definitely not my best self which I feel shitty about, because I like my friends to feel good and safe while they're with me. I am a bit older than her and I know that she admires the experiences I've had in my life. I am given the distinct impression that it has turned into a dynamic where she is desperate for any scraps of approval I toss her way and I'm kind of cold otherwise.
She keeps inviting me to things, including her upcoming birthday, and I'm not sure what to do about it. On one hand, I want to show up to these things because I know she doesn't have a large friend group, but on the other hand, she deserves to have friends show up who aren't icy bitches. On the other other hand, WHY CAN'T I JUST BE NICE TO HER!?