thoughts - how do you get their cc statements. if you get them from her she can just give you the clean ones. can you get a credit check done that lists all of her cards? is there anything else besides cc that i should look to get. what about the fact that she spend 3k in rent and 750 on car payments but wont pay for her kids expenses because she is living way beyond her means. is that an argument?
You go for a very thorough but deliberately reasonable discovery. You ask in a Request for Production her credit card, checking account, saving account & money market statements for the last six months. You ask for receipts for airfare and hotel that she not only paid but where she resided, making the wording specific to turn up anything where new boytoy fronted the cash.
You keep it reasonable in length -- recent history -- to avoid her objecting you are being punitive. Assume you will have to go before a judge with a Motion to Compel, which you chase after she fails to hit her discovery dates.
Talk to your lawyer about specifics on local procedure. You get a longer window on discovery if you are chasing a mod versus an enforcement, as enforcement hearings can usually get scheduled much earlier, so discovery assocaited with mods can be more thorough. However, you can create a bit more of an adrenaline rush on her by going the enforcement route.
Also, make sure you chase fees. In some states, like TX, award of fees is mandatory if the other party fails to pay their ordered share of medical expenses, as the law assumes it's defacto denial of medical care for a child. Even if not in your state, it will likely pi$$ off the judge against her.