How to rebook a cancellation?

I booked a client to watch her dog in my home, but then the drop off time wasn't able to be accommodated by me so we agreed to cancel the reservation so she could find another sitter, and she was issued a refund. The client contacted me today saying she is now able to accommodate the drop off timeframe and she wants to rebook with me, but neither of us can figure out how to do that. Help!