Forget about trapping, if she has a litter in your attic. Do the following:

1. DON'T close up any openings from the attic to the outdoors, just yet.
2. Set pans of ammonia around the area where you hear activity from the
litter or others.
3. Set up lights and a radio (playing fairly loudly) in the attic area.
4. Visit the attic a couple times per day, making plenty of noise when you
do. DON'T confront the adults, however.

WIth the above, the invaders should be gone within a couple of days. Has
worked for us in the past.