She is completely taking advantage of your money. I don't know how you can force her to stay in an affordable hotel. When I looked up nesting, the example they gave was an apartment that the parents rotated as well as the home where the kids lived.
You need to take control of the finances. Can you remove yourself from the credit card? There needs to be a plan where she pays for herself and you pay for yourself. Both parents need to agree prior to signing kids up for things... however, without a legal agreement in place, I'm not sure how this would all work.
Have you met with any lawyers yet? Many have a 1 hour free consult.
