Hmmm I think professional help is needed.
Firstly on an income of 50k, i'd be interested to see what kind of rent your paying that doesn't leave you with plenty of disposable income.
An average mortgage/rent of flat is prob about £500 for most areas, apart from the big smoke. So that's roughly a third of her wages, and prob a quarter of yours. That leaves £1500, now food you could easily spend £40 a week and survive, so lets take £200 off that £1300. Now petrol and bills maybe another £300 pm. That's £1000 left so where does it go???
My guess would be that your living the highlife(if you cant afford a lavish wedding don't do it) and it will lead to ruin. She clearly still has an issue (in debt) if she pays for nothing, and the extra £500 disappears!
Sorry if it seems harsh but my partner and me, earn at least a 5th less that you. Im paying the mortgage whilst she is maternity, and all bills, my petrol etc and I still have £200 to play with each month for next 5 months to keep me sane! Plus I save a fair bit.
You need to take control here! Get a spreadsheet and put all your joint bills on - food shopping, rent, water/gas/electric/phone, council tax. Then get joint bank account and agree to put 50-50 into it and pay that out of it.
The money left for each of you, is yours. You can pay off your debts, she can live her life. If shes then having financial issues of course you can help, but I don't understand how or where this money goes or how you don't know.
My wife sometimes says - ive only got £50 left with two weeks of month left, I ask why, and normally she can explain what she spent more on but she never asks for more, just cut cloth accordingly.