You seem to have some things in your favor. But either way you should CONSULT with a LABOR ATTORNEY.
I have heard that in order to participate in the "blanco" mode, and pay taxes on their income, domestic service employees must work at least 3 days a week at the same address, and over 4 hours each time. These figures may be slightly off, but I know there are some minumum requirements.
The way I recall it, anything less than that may be considered a "loop-hole" that doesn´t require any registration or taxation.
So you would not have broken any law, and she would need to PROVE that she was there over and beyond those specific time limits.
What you have in your favor is those bank payment receipts. It will be very hard for her to convince a judge that you were only paying her for one work day per week, while she was not demanding payment of the other 4 days!!!
Ask your lawyers if by accepting every weekly payment without claiming outstanding pay, (through a "carta documento,") she has locked herself into having to admit that she was only working that single day each week.
Another trick you can pull is to try to meet her alone, and "WIRE" YOURSELF or your place with an AUDIO or VIDEO RECORDER. Ask your lawyer if it can help to get her to admit she is just trying to shake you down. You may need a court order, and that may be through an "penal" lawyer, not "labor". (many lawyers handle the different courts).
Other option: sell apt. and re-invest abroad and off the record if possible. You can buy an apt in Montevideo, put it up for rent, and rent something here for the same amount. That way the justice system can´t put a lean on your property, which they can do in a few months if the case is filed.
Ask your lawyer about the chances of a favorable "mediacion". The mediator is a neutral attorney who may side with you, upon showing the bank transfers. You can actually be spared of any payments except a 50/50 on the mediator and your atty. fees.
If you don´t "win" outright, you may reach an agreement, without accepting any wrongdoing. This outcome is a legal settlement, bound by the courts, meaning she is out of your life and the case is closed.
If you need to settle, try to convince her that any settlement, no matter how small, is safer than a possible loss in court (becasue of your e-payment slips).
OK, best of luck.
PS: for ALL your employees and help, YOU NEED TO GET PROPER RECOMMENDATIONS!! Evangelical churches are where you can find many decent, honest workers.
