A "like" in support, hugs to you and your furbaby. Both of my previous dogs each had ACL surgeries (TPLO) when they were around 10-12 years old, and they both went on to live a few more good years afterwards. With a cardiac condition, though, I can see how your worries increase about anesthesia. Definitely have pre-anesthetic bloodwork run beforehand. If this place is worth their salt, they will have a blood pressure monitoring system, ECG, pulse ox, IV fluids, a good perioperative pain management protocol, and a technician there during the surgery who will be actively checking on your doggo throughout the entire procedure. Post-surgery, there is the recovery time at home where you'll need to have your house set up to keep her quiet and away from the other dogs because she needs to have very controlled activity for weeks afterwards (although you might be doing that already?).
Not an easy decision, I totally get it.
Open up a Barclays Arrival+?
Other ideas - Discover checking gives you 1% cash back on up to $3000/mo. Will the vet will take Discover debit cards? It would take some time for the debit card to get to you if you opened an account today, but ACL surgeries aren't emergency situations and are often scheduled weeks out in advance. I personally MS my Amex Gold some, but don't know if this is an option for you.