Is it ok to get independent feedback before handing in thesis?
One of the objectives of gathering professors, postgraduates, graduate students and undergraduates at an university is precisely to encourage working together and cross-checking. Nothing wrong here.

If another graduate student in interested in your work, good for you! Perhaps the basis for future collaborations. If she helps you out by helping proofread your thesis, she is certainly entitled to an acknowledgement of the help in your final writeup. And you should also lend a hand, either to her or some following students, in gratitude.