Agreeing with Luna here, the vet office didn’t even try to contact you to say that following the surgery (irresponsible of them. If they aren’t going to remove them, who would? They should!), so clearly it’s not completely your fault! I asked myself the same question with Wick’s neutering because his stitch is still in!
I don’t have any experience with stitch removal unfortunately, but use the same cautions after a procedure as you did following Goose’s spay. Since it didn’t get infected, I think that’s a sign that you take good care of her and she’s in a clean environment to say the least!
It’s an uncomfortable subject to bring up, but I would ask the vet why they did not reach out to you following the surgery, and if there can be a leniency on pricing of the needed procedure, if there needs to be a payment at all. This vet office needs to have patients point out these errors and take action on them so they do not make them in the future.
The answers provided in this discussion are for general guideline purposes only. The information is not intended to diagnose or treat your pet. Seek the advice of your veterinarian or a qualified behaviorist.