First of all, if you did have a change in income your ex is allowed to ask for an increase in child support including back child support from the day you started making more money... and yes the judge will grant it to her. Now on the other end, if you ever make less money you can ask that the child support be decreased. For the tax returns, most likely the judge won't change that since it was already agreed to in the divorce. She's probably just pissed cause she's not getting the extra $300 stimulus check for claiming a child.
Secondly, just because she married a rich man it doesn't mean he pays a penny for the child. He probably doesn't want to support the child which is why she is asking you for more money. Hells, the fact she doesn't have a lawyer makes it seem like the sugar daddy doesn't let her spend his money either.
BTW- Good luck hiring a lawyer and only spending $10k on it. From the sounds of this chick she is crazy and is just trying to piss you off so most likely this would drag on a long time. I'm on the opposite side and my ex husband was dragging out the custody case even tho he's the one who sued me and it's almost two years later and over $75k in legal bills I've paid.
For anyone else who is bitching about what you pay in child support, you seriously need to STFU.
Children are expensive and if you can't afford them or didn't want to have them then you should have worn a fucking condom. I fucking hate hearing guys bitch about paying child support. If the amount was court ordered, then obviously there is a reason for the amount set and the judge says you can afford it. It might seem like you are paying a lot of money to your ex but I'm sure it's not enough to cover half the expenses. Child support covers a portion of the rent/mortgage of the home the child lives in, the utilities for the home, groceries, clothing, school supplies, field trip expenses, gas for driving the child to and from school/day care/doctors visits/etc., cold medicine/prescriptions, toiletries, diapers, formula... I can keep going because there are a ton of other small misc expenses that I'm sure you don't think about. Chances are your ex is still spending more than you are on your child.