I'll take another approach on this MI Trapping - since you now confirmed bats flew out, you at the least have a potential bat issue (depends on if the client thinks its an issue) that stands in the way
of sealing the holes as you were planning to for the squirrel issue.
A hole right at the peak where two fascia boards meet is a great spot, mostly in my country it isn't the large colony location, but a good spot for smaller colony or a few solo bats. Depends on how much recess or space they can reach.
Anyway, you now have documented bats, so you I assume are having a bat conversation with the clients whether the sounds were from the squirrels or the bats.
Related to the squirrels, you mentioned the catch rate went to zero, was this up on the roof, down in the landscape or other and did the hole in the fascia look like one gnawed by the squirrels are a construction gap or defect or woodpecker damage or other?
Just questions, either way again, you've got bats.....
I'm assuming you are trying to confirm if the squirrels were the noise so you know if she isn't hearing noise you are done squirrel trapping and just have the bats within the area to work with.
Justin