What should I do about a friend who has stopped talking with me?

So I met this girl at a function at my college. I am also a girl but didn’t know many people and she was new too and didn’t know anyone and we talked and became friends back last October. Anyways we were friends until I had to move away from an internship in mid November and it lasted til early February. Well I saw my friend after 2 and a half months, I was suppose to visit in December but I got busy with work and didn’t come. Well I noticed now, she isn’t responding to my text messages anymore and doesn’t seem interested to hang out or eager as she use to be back when we met in October. I’m kind of sad because I bought her a $15 gift for her birthday a few weeks ago but she still doesn’t seem as eager to be my friend. She ignores my messages even though she goes on Facebook as I see. When I saw her a few weeks ago she had briefly mentioned she feels she has met friends now since moving here back in October but I didn’t know what she meant by that. What should I do?