Default payments

I offer a course and a membership program. A potential client wanted to join the course and emailed me to see if she could get a discount. I said I don’t offer discounts but did offer her an extended payment plan which she took. Then when I was launching the membership program she asked if she could get a discount on the membership program because she was a member of the course. I gave her a small discount. Then 4 months after join the course and 2 months of joining the membership program she defaulted payments on both.

The membership program gets automatically canceled after 7 days of the payment not going through.
3 weeks later I am relaunching the membership program and explained the cost was going up nearly 50%.

She emailed me to say she wanted to rejoin, at the lower cost, but won’t be able to until next month. Could she get still get the lower price.

Then because I said she couldn’t she has been bombarding me emails.
Each time changing her story about what she was asking me and what price.
It’s making me very anxious and now I don’t even want her in either the course or the program.

C Client payment defaulted and wants to rejoin
T She is pushing my boundaries
F Anxious
A Ignore her many emails
R I continue to feel anxious

How can I handle this situation?
Thank you.