I know your heart is in the right place, but she is disrespecting you big time. She is dumping her problems onto you.

You've gotten some good advice from others here.

If this were me, I would have a hard time simply cutting off a friend in need.
Why don't you send her an email stating that all her emails are beginning to have a negative effect on you, but you still want to be there for her and are willing to read and answer one email a day.

Then send all her emails to spam, and at the end of the day after you have taken care of all your needs such as eating, doing dishes, showering or whatever, go into your spam folder and without reading them, cherry pick exactly one email to respond to. And keep it to one.

And also suggest she gets counselling. Tell her they are more prepared to help her than you are.