I will say Tteok is such a spoiled brat, he’d be absolutely THRILLED to be a single bird. He’s not been around other cockatiels, but so far he’s not enjoyed either quakers or a cockatoo 
I do think it’s possible to have a single bird, but a lot of it depends on a lot of variables: The bird in question, their bond to you, your ability of time commitment, space, whether they can entertain themselves if you’re not available…
So far, it sounds like you’re doing so incredibly well with her, even with her being a single bird. I’d say give it a year from now if anything - you’ll be well-settled in the apartment, have an idea of your schedule since you’ll be off campus, etc.
I do think it’s possible to have a single bird, but a lot of it depends on a lot of variables: The bird in question, their bond to you, your ability of time commitment, space, whether they can entertain themselves if you’re not available…
So far, it sounds like you’re doing so incredibly well with her, even with her being a single bird. I’d say give it a year from now if anything - you’ll be well-settled in the apartment, have an idea of your schedule since you’ll be off campus, etc.