calling mentors by first name?

[the defenestration]

My graduate student mentor has been quite influential in my decision to pursue graduate study in biology, and as such she is mentioned a couple of times in my research statement (basically an SOP but only talks about my lab work). Is it appropriate, after introducing her by her full name, to just call her by her first name? My sister, an English major, recommends that since it is formal writing, I should refer to her as "Ms. Last Name." I would not call her that in person, so to me that sounds odd. Thoughts?

[Rachel B]

I agree with your sister. Since you're presenting your statement to other people (not directly to your student mentor), it's a better idea to go the more formal route.

[kaykaykay]

I agree with your sister . I got the same advice from a prof who proofread my SOP.

[the defenestration]

Thanks guys