The correct answer here is "suba" because It is required a verb in its singular female form. So the verb "subir" is the correct option to fill in the blank.
Another possible option would be "estudie". However, If we fill in the blank with the verb "estudie" the sentence has no sense:
- ¡Ojalá que ella estudie a ver nuestro apartamento!
As you can see this sentence sounds odd that's why the verb "estudiar" can't go there. Besides the verb "estudie" is intransitive so It can't have as a complement another sentence like "a ver nuestro apartamento". That doesn't happen with the verb "suba" which is a transitive verb that selects a complement so the correct option would be the following:
¡Ojalá que ella <em>suba </em>a ver nuestro apartamento!
