Definitely airway. I am no expert (1st semester), but in my opinion, airway is most important because most adl's require more effort from her than a question/answer interview that you witnessed, and that in turn affects her mobility, nutrition, autonomy, etc on a daily basis. If you can't breathe, you really can't do anything...yk? Also, with the sputum, she'd have a risk of aspiration. So for interventions, you could deep breathe and cough, bed at 30 degree angle, maybe send sputum to lab since it's green? I'd say increase fluids, but with her cardiomegaly, I wonder if that might be contraindicated...like I said I am just first semester myself.
I know in my school, they look for the major diagnosis, but want others as well if the problems are there...so maybe you could include a sub nursing diagnosis of activity intolerance and/or other things you see as important. I know my instructors would rather too much than too little...it shows you are really thinking it through.
good luck and I hope I've helped.