Do you know what grade the mummer is and what is the exact cause of the mummer? Your normal vet won't be able to tell you this, you will have to a cardiologist to find out the full extent of the mummer.
If its a mid - low grade mummer she should be ok for a short surgery if they monitor her heart closely during the operation.
Our first boxer who is now at the bridge had a mummer grade 1-2 caused by Sub aortic stenosis, never caused him problems his whole life and he successfully underwent several surgeries throughout his life.
Finnegan our current male also has a mummer again low grade at 1 - 2 but his is caused by Mitral Valve Regurgitation, he has recently had surgery with no issues either.
Regardless of whether you get her spayed or not you should have a cardiologist examine her so that you know exactly what your dealing with, and it should be examined once a year. The cardiologist will be better able to tell you whether or not her mummer is too serious to under go anesthetic.
They are graded 1 - 6, 6 being the most serious.
Good luck and let us know how it goes
Adelle
Adelle,
Finnegan, CGC & Nessa, CGC
Boxer Buddies Rescue & Adoption Inc.