How to tell someone they are annoying you big time w/out hurting them?

I met this girl at uni this year, she is a nice person but is v. dependent on me, if i cant cometo a lecture she doesnt go either, always wants me to drop her at her college after cl, wants me to meet her to study but she just keeps talking about how stressful her life is, ( we both do the same course, i work part time on top of that, she doesnt work at all),and about a situation with some friend of hers whom i dont even know, she wont actually disclose the situation but complains about it, basically she doenst trust me enogh to tell me what it is but uses my time to complain aboit it, ironically she thinks i talk too much and that thats why we dont get much study done!!!!, the teachers dread her, always asks irrelevant questions..several times, Today, in cl she asks if she can drink some of my water, i hand her my trusty water bottle and just as she was about to drink turns and says "oh wait but, its clean right?, do you think she is anoying?what should i do, tell her