She is on my course, and I know that she is single.
She doesn’t come to the lectures that often so we haven’t really established a solid connection.

On occasions she told me that she liked pool and climbing, and when I asked, she gave me her phone number if I want to do any of those things.

Three different times I texted her for that, but all three of them she was tired/had something else scheduled. 

None of the times she mentioned rescheduling like “hey, let’s do it another day, how about this date”.

Therefore it was established to me that not only she isn’t attracted to me (which is understandable and something I can deal with), but she doesn’t really want to even hang out with me.