When a someone has initially friendzoned you in the first place, the chances of them actually being interested in you later on isn't all that likely. I'm not saying that it can't happen because it most definitely can and I've seen it happen, but I wouldn't put your hopes on it too much. So since this girl has friendzoned you already, she is probably taken aback by your gesture and gifts because to a girl, those are signs that you are interested in her and she clearly doesn't want that.
From your description, it sounds like she was just being friendly with you. Talking to you every night does not automatically mean that she likes you that way. I have a few guy friends who I talk to almost every night and I'm not interested in them that way. And if one of them were to suddenly get me a box of expensive chocolate and stuff like that, I'd pull back because I'm worried that I'm sending them the wrong message. This is most likely what your classmate is doing: She realized that she was probably sending you the wrong message and decided that she should stop.
If you giving her those things were only meant as a gesture friendship, then you should explain that to her if you want to save your friendship. You just wanted to show her your appreciation and that was it. You want to be friends and nothing more. But if those gifts were meant to show that you like her because you think that her talking to you means she likes you back, then you need to give her some space and understand that she probably doesn't like you back.
Although her going offline on Facebook when you go online isn't a really sure way to tell whether or not she's actually trying to give you the cold shoulder. To know for certain, she has to be doing this for probably several consecutive times and when you're in person, she tries to avoid you or make your conversations short. If she shows those signs, then what I have stated above - about her not wanting to give you the wrong idea - is most likely the case and she's afraid that you like her since she doesn't like you back. If she behaves fine after that, then it was probably just a coincidence.
Anyway, the main point is that don't assume that her talking to you means that she has changed her mind about friendzoning you and you have the thumbs up to shower her with gifts. Trust me, rarely do people change their minds about friendzoning others. I have been on both ends of the friendzone: The one friendzoning other people and the one being friendzoned by other people. And yes, girls can be friendzoned too. From my experience of having been on both ends of the spectrum, I can tell you with confidence that it's highly unlikely that she will change her mind. But beware, they may still flirt with you and are friendly with you because they know that you like them and it's easy to use you. Don't be misguided by those as signs. I know that it sucks to be told this and it's painful. I've been through it a lot, but in the end we have to accept it. It's a waste of time and energy to like someone we can never have. So unless those gifts were just a gesture of friendship, you need to let her be for a while or else she'll think you're creepy and whatever interaction or friendship you had with her is over.
Anyway, good luck with everything.