Between a rock and a hard place with my foster

I’ve had my foster dog for two months and six days of the longest two months and six days of my life. I already have a full house with my own dogs, kids and I work full time as a single parent. My problem is that I rescued this dog from a dangerous situation and I found the rescue group that was willing to network her (rather than taking her to the shelter). I have let the rescue group know I can’t last much longer. I would like to take her to the shelter before I fall apart mentally. I spend my weekends driving her to meet families that don’t adopt her (I only have the weekends to run errands, clean the house, grocery shop, and go to the gym to decompress my stress). I am coming undone. I let the rescue group know this and they reminded me that this was my fault - I rescued her. I said I would foster. They went as far as to say I would miss her when she was gone and all fosters are overwhelmed like this.

Meanwhile I am fantasizing about taking her to the shelter. What would you do?