God bless you for taking control of the dog. I would check online because I know that in my area (California) there are groups that take in rescues. There are also no-kill shelters, or may well be, in your area. You may well want to keep her but doing what you have done so far is very loving. Good homes exist out there where she'll get a lot of love.

Since you are not the owner of that dog, you have no right to try to place her, sell her or do anything that may be held against you by the lawful owner of that dog.

The only thing you can do is to call the authorities or the local pet shelter that needs to take the most appropriate action.

It is sad that people dispose of their pets once they have no more use for them but even if you took care of that dog for s few days, you are not the legal owner of it.

Screw the previous "owner"!!! If you can find her a new home, go for it! Post an add with her picture, describe how sweet she is. Call a few places and see if you can find someone to foster her.