I suspect you're right. She probably wanted to deposit $11,000 and take $1,000 in cash and the bank wouldn't do it until the check cleared.
The employees probably said something like, "We can't give you cash right now until the check clears. It's very unusual and it might be counterfeit so we have to be careful". That's much more likely than, "It's counterfeit. We won't deposit it".
facts are racist