I've had a couple of nippy momma's in my time. What I do is get one of these from the dollar store, distract her with something moving so she turns away from you, then quickly tail grab her and dump her gently in the container (I put some bedding in there first). Don't dangle her a long time, just have that tub right there beside her enclosure so it takes but a second really. Snap down the lid and there you go, no rattie bites. When it comes time to put her back just lower the tub in, unsnap the lid and gently slide her out (that way she can't turn and nail you in the close confines of the holding container).

Ratties are tricky, but I'm trickier!