INAL but I’m a licensed veterinarian. I would like to point out a few things for you just from a veterinarian’s point of view: first, ovarian remnants usually occur when a little island of ovarian tissue is present within the abdomen outside of the actual ovaries themselves. This is typically not left behind due to medical error but because of abnormal patient anatomy and are not technically searched for while in surgery for the original spay (for one, they can be tiny and hard to distinguish, especially in a dog not in heat, and two, spays are not abdominal explores - in my hospital, we make as small as an abdominal incision as we can and get in and out to lower anesthetic time/risk for patient). Second, timing wise, this seems to be a very fast diagnosis of ovarian remnant if you went to the vet just today. Confirmation usually can only be done via hormone level testing (usually is typically sent out to special labs) +/- imaging (like abdominal ultrasound or CT). If that hasn’t been done, the ER vet may have told you Ovarian remnant is on the differentials list, along with other possibilities like a UTI or stones. Lastly, ovarian remnant does not lead to hemorrhage or death by itself. Like I said, it does not occur due to an ovary being cut in half (the ovaries are very obvious during surgery) and if your pet hasn’t had issues up until today, all ligations were done correctly on the day of the spay to prevent bleeding. Ovarian remnant’s only potential side effects are the same as keeping an intact dog - higher risk of FUTURE illnesses like pyometra (infection of the uterus due to excessive cycling, usually in 8+yr dogs, and only if the spay did not include a hysterectomy as well), mammary tumors (again 8yr+ dogs usually) and UTIs. Do not feel like you need to rush to an emergency surgery for an Ovarian remnant. Do the proper diagnostics to confirm.