I can’t say I have experience of exactly this, but having been through divorce I have some knowledge.
Do you not have the original agreement you both signed when divorcing? AFAIK this is as legally binding as any contract and therefore she willingly agreed to it as an adult.
The burden of proof I would think surely lies on her to prove her case.
I wouldn’t spend anymore on legal fees especially if she is taking you to court, she has to prove her case not the other way round.
If it’s all untrue as you say, she won;t be able to prove it, and I assume you can go back in your bank accounts for the past X years to prove otherwise?