Professorship Duties

How odd that in the last two weeks I have had two requests that normally would be fulfilled by a professor. Last week, one of the profs who is unfamiliar with the program asked me to advise an incoming graduate student. Hrm! I thought that would be fun and exciting. I spent some time on it and really enjoyed it. But, the other request has unnerved me a bit. One of the undergrad RAs asked me to write a letter of recommendation for her. Jeesh! I've only done this once before when my star student listed me as a reference for a babysitting job and the potential employer actually emailed me. Plus, I don't know if I should do it because letters of rec should normally come from a professor, not a graduate student. But, on the other hand, I probably know her better than anyone because she's worked in my lab (which was not really being overseen by any professor). I'd love to write the recommendation letter for her, but I'm not sure what the formula for doing so would be. I suppose I might ask my advisor, but only after I have my thoughts gathered. Yeesh! This will be interesting.