You did something nice for someone. She didn't appreciate it or even acknowledge your effort and that's not your fault. It doesn't make you a chump either. We can't dictate other people's reactions and had you known she would have behaved like that maybe you'd have made a different choice, but you didn't know. You were kind for your reasons not because she deserved your kindness and sometimes that has to be enough.

You didn't really lose anything so don't keep reliving the situation. She's probably moved on the spread her misery elsewhere. You could have given her a lung and afterwards she'd probably tell you the shut up with all your wheezing. Now that you know the next time just lean back on the wall and videotape her exit to make sure she doesn't damage your car.

Or you can look at it like she's a miserable person who may have had to deal with some miserable circumstances in life and maybe misery is all that she has to spread. You were compassionate and didn't add to her joyless cloud.