First, I’m very sorry for your experience and feelings of inadequacy. We have all been there. Through this, you will be a better provider and a better person.
I am curious, though, if there was any diagnostic imaging ordered? And if her other vitals beside spO2 were stable and within her baseline? SOB, desat to 80’s, anxiety (above baseline of being needy), and I immediately want a CXR (which would not show a PE, but other things could then be ruled out), and an ABG. Nothing on CXR? Start heparin and get a stat CT chest. No one ever expects a patient to get a PE, but there are more things that can be done to catch it and prevent it from being fatal. Yes, her sats came back up, but with supplemental oxygen now. She sounded wet, so lasix seems appropriate given her CHF, but still with her symptoms, more should have been ordered and done to figure out the exact cause of these things.
This is not your fault. But you can use this tragedy to learn and be better. You are truly compassionate and that will take you far. Don’t lose that.