Long-Term Puppy Stay: May have to cancel?

About two weeks ago, one of my clients referred me to another woman who needed a sitter for three separate bookings for four-month old puppy (five days, this week and next; and then two weeks in late July/early August). I was greatly excited about this and during the meet and greet didn't suspect any poor behavior, outside of normal puppy play.

Nope. Within the first 10 minutes I had to put her in a time out due to her jumping up, biting and barking despite my commands to have her stop. After taking her out of time out, she was right back at it, and went back in time out where now she is sleeping. I don't mind the normal puppy behavior but the lack of listening to my commands is making me feel like this may not be worth the funds and that they may be better finding a sitter who would not mind having to train the pup as well.

I would hate to have to cancel this because I truly feel that I can help to make a difference but this pup needs almost constant attention/teaching and I worry that because I won't be able to give her this, she may become more destructive (biting, ripping things up, barking, etc.). Also the owners are an elderly couple, so I would hate to have to have them find someone else when they clearly planned and put their trust in me.

Any insight/advice would be helpful. I just wonder what my 'limit' should be when sitting, especially long-term. If this was one or two days, I think I could justify spending more time and effort working with her each day but I can't. What do you all think? Thanks in advance guys :)