Can this have both a positive and negative meaning?
I say: Are you really going to let one girl change your life?
Since change could mean good or bad.
I don't think the question itself has either a positive or a negative connotation. It's a straightforward question. There must be a reason you're asking the question and that reason will give context. The context is likely to be either positive or negative.
Remember - if you don't use correct capitalisation, punctuation and spacing, anything you write will be incorrect.