My neice swore she was going to turn herself in on more than one occassion and never did. When she got picked up she tried the "I was gonna" line.
I agree with impurrfect - the kids won't understand the back and forth. I have a foster-neice who has two kids living with my sister - similar to you, she filed and got custody. In her experience, her foster daughter wants to see the kids for her own gratification and to manipulate my sister, not becuase she suddenly wants to be a good parent. If she does want to be a good parent, she can start by straightening out her life and turning herself in. If she hasn't done that in 4 months, I wouldn't hold my breath.
I think your initial instincts are correct. I know you love her and it's hard to hear kids saying they want mommy and daddy - and at the same time, tough love means doing the right thing even if it isn't gratifying or rewarding. I'd say, stick to your guns and your initial inclination.
I hope this doesn't sound too harsh. I think you have a good head on your shoulders and have the right instincts - don't let them talk you out of what you know is right.
Prayers for clarity and peace...