I agree with the others. She doesn't pay your bills or support you, so MYOB.
I also agree that when someone is unhappy, depressed, hurting, it sometimes comes out in picking at others. You are so compassionate, you are trying to find the root reason for her tirade and that speaks volumes about what a generous nature you have. If she is/was a nurse, used to caring for people, being in charge of others as well as herself, then this nastiness may well be partially stemming from an attempt to feel in control again. BUT, that does not excuse it.
I think that just letting it roll off your back is a good idea, but perhaps a gentle, "Really, I have a handle on my finances, not to worry." Wouldn't be out of line.
Take care, God Bless, and don't forget to post pics of your Hot Wheels quilt when it's finished.
{{{HUGS}}}