Not a right fit.

[Inspired by Reggio]

If this is a client that you are not wanting to 'invest' in fixing any issues with than I would just leave out that things are not working out ~ cause than they are going to be defensive and even more awkward ~ and personally I would just let them know that permanent care is no longer an option without getting into details of WHY and let them just assume it is because you filled your spaces or something something like ...

'Just wanted to drop you a line to confirm that as per our temporary arrangement care for Johnny Doe will be finished as of August X, 2012. Due to changes in the program a permanent care option will not be available at this time. If you ended up not needing care as long as initially anticipated due to your current provider recovering or choosing an alternative permanent solution please remember that X days notice is required Yours kindly Ashliegh' or whatever you have agreed up notice wise on their end.