What is the best way to handle a person like this at work?

I need some advice for the dilemmas I am dealing with at work recently. So I am working as a summer intern while I found out this girl who went to school with me also working in the same division. I didn't like her before that because when we went to school together, I gave her my number at least 5 times, she never saved it even though she's pretending she would call you to hang out. I email her see how's she is doing once in a while. but she never replied back. And when she need help, say she need some information about a class. She would email you and never said thank you. The last time I contacted her was for the graduation, see if she's going and she still never replied back. So I stopped talking to her even I saw her at the graduation. And now we work together. She asked for my number, I thought she wouldn't keep it but she did. However, she's calling and texting me everyday so I could cover something for her. What pissed me off more is she has her own project, but she's taking my project because that increases her chance to meet people and get a real job. And my mentor really like her because she says all the things that makes my mentor happy. I don't care if I am working with her, but she's screwing my chance to get a real job. I want to know what I am supposed to do because I really want to slap her damn face when no one's around. Please help!!