Sharing a master thesis with a third party before the final exam
The detailed specifics of this will likely depend on her university's policies.

In most situations I am aware of, the student retains the copyright of her thesis. She should be allowed (from a legal perspective) to distribute her work in whatever way she sees fit. Likely the best thing she can do in this situation is speak with her advisor. If her advisor is desiring to publish any papers from the thesis, he/she may not want the work shared with a third-party. 

It may also be possible that the student in question here only send a portion of her thesis to the third party. A pre-print, if you will. It should be sent with a note specifying that the thesis has not been defended yet and is subject to final revisions and review. Open and full disclosure is the best option here.