Hi Angela,
I agree with Darren's post on this issue, move them ASAP, or risk loosing the contract and good name of your company.
I work part-time for a contract commercial cleaning company, and if the customer doesn't want a cleaner on their site, then that cleaner doesn't go back there, end of story, as the customer is paying and my company won't send anyone back if the customer says no.
It does sound like this particular cleaner may be a problem for you and your other cleaners. if they've only been with you a month are they on a three month's trial period? As most jobs even part-time now employ on this basis. I would move them and make sure they are supervised and monitored.
Good luck Phil.