From your description, it seems that your classmate's offer to get coffee may have been more of a friendly attempt at small-talk than an earnest desire to get coffee and spend more time with you. From what I understand:
- She casually suggested that the two of you should get coffee sometime
- You have attempted to schedule multiple times to get coffee
- Each time she has said that it will not work for her and does not suggest a time that will work for her.
She may truly be busy and not able to easily schedule a time with you, or she may just be declining your invitations for coffee because she is not interested in getting coffee with you.
Instead of organizing the time/place for her, why not ask her to decide a specific time to meet up? I have had done something like this with several acquaintances and it helps to resolve any confusion around the other person's true feelings since they have to make a decision.
Hello! I know your schedule has been hectic lately, but I would still love to get coffee with you. Is there a certain day/time that we could meet for coffee in the next week or two?
From your interactions so far, it sounds as if she may not be comfortable being direct with you and telling you "no" if she doesn't want to spend time together. So if you want to be polite and give her an "out" that doesn't force her to be direct, you can add something along these lines:
And if you're busy, no worries!
If she has truly just had scheduling issues, then this will give her an opportunity to successfully organize something for the two of you. Almost anyone can slip in a coffee break at some point in two weeks. Alternately, if she simply isn't interested in getting coffee with you then she may say she is busy again. And at that point, I would interpret that as her not being interested, despite her initial suggestion to get coffee.
I have been on all sides of this scheduling issue (being too busy, being disinterested, making plans with a busy friend, making plans with a disinterested friend). In my experience, some people are too kind to say "no" so they continue to "be busy" to avoid hurting my feelings - with this strategy it at least helps quickly determine if they are busy or just indirectly saying "no".