Awww sorry about your results. But keep at it.
I think you need to make heeling the biggest most important thing to her.
Is she toy motivated because if so it might be time to keep her favourite toy for heeling only.
If not I'd start heeling with her food bowl in my hand, with warm BBQ chicken in it, treat when she is right up beside you.
You may also like to learn how to target to a stick (long handled wooden spoon does the trick) and use this for heeling practice.
Do you talk to her when heeling? I'd be making my voice happy and bright.
Use your conditioned reinforcer for heeling too.