It did sound like you had the best intentions, but most of the times when we humans play around with mother nature we do more harm than good. I'd do some research for a rehabilitation center near you if possible. This would be the painteds best bet.
Please read through the forum and main site thoroughly before purchasing your RES. They are very rewarding pets to have, but they do require a lot of care and maintenance to live long healthy lives. Just to keep in mind, even by purchasing one RES, you will still have to upgrade eventually from your 55 gallon tank to at least a 90-120 gallon depending on whether you have a male or female.
Good luck and let us know how we can help.
