You catch more flies with honey....Personally I'd talk to the daughter. Tell her how glad I am that she's helping her mom because I really need a break. How glad her mom is to have her back around etc.... OR you could have the talk with both of them.

Something along the lines of since her daughter is back you don't want to intrude so you will just help with the dog.

You are not in an easy spot and I wish you the best.