As far as getting her to trust, I would just make sure you approach her at her level and not from above. Hold out your hand with some meal worms. Might have to wait a good long time, but eventually she will learn that you are not going to harm her. Muscovy girls are kind of standoffish unless you've got something they want.

Mine will come to me for meal worms or if I'm shoveling dirt (they stand around to see what treats they will find). They also don't mind if I pick them up briefly. For part of this spring 2 of my girls decided they were sleeping in the chicken coop and would stand by so that I could pick them up and put them in (if they didn't get in there before the auto door closed). They quit doing that now and have decided to sleep in the duck house again. They are quick learners, so I bet she will figure out super quick that you are there to help.
If a boy, they are much more entertaining and usually will come see what you are up to. My one drake follows me around and is sometimes very annoying, but has lots of personality.