Since she just had major abdominal surgery, I don't think she is challenging you. Everything does get moved around or touched in there and it may take some time for things to normalize. Urinary incontinence is one of the risks of spaying but it doesn't seem to be too common long-term. It would be possible for her to have gotten a urinary tract infection after surgery also, so she may have a hard time making it to her pee pad. Your vet might want to do a urinalysis or they may say to wait awhile. I would call and ask what they would like you to do.
