My 8r Yo Mom Is Going To The Doctor In

My 8r yo Mom is going to the Doctor in a few days for an Echo and follow up to see the progression of her Aortic Stenosis. She has been short of breath on the slightest walking, but no edema in her feet and legs. She took her Pulse ox and at one point it was 88 and then later 95. What types of things should we look for? Her Doctor is aware of the symptoms, but not the oxygen rate. He seems ok with her waiting until Monday. At what point or symptoms should we look for as a medical emergency?