I would do the dead minimum to avoid guilt! Call the local shelter and put in a found report and put an ad in the paper for 2 days that says, found dog, wandered into yard, please call......

How are the antibiotics working?? I'll bet she's feeling better and better everyday.

Oh yeah, I would charge the owners, if they show up, for the surgery (before they take her) and that will probably solve the problem right there.