She needs to find where they are coming and going from and plug it up while they are gone. Glad to hear she doesn't want to kill them. Too many people are afraid of bats.

Claudia,
She can hire a professional if she can't figure out herself where they are getting in and get on a ladder and hammer up wood in the middle of the night.
She should call a pest control comapny and ask what they charge for a "Bat exclusion". They put in a fixture that will allow the bats to get out, but impossible for them to get back in.
Then they will find a new home for the winter.
Good Luck!

Yeah, I think I would also hire a pest control person to handle the extraction. They're much more trained with these things than we are...if you get the right ones. Check them out first.

If your friend knows anyone that installed a bat box that failed to attract bats (very common problem), she could call them over to scrape up some fresh bat poop to sprinkle at the base of wherever they installed their bat house. Bats find roost sites based on smell, they like to roost with other bats. Using poop as a lure is about the only way to encourage bats to consider your place home. Of course she probably just wants them gone.