Perhaps letting go with her can stop that backward spiral and bring you loads of peace. Just a thought. Baby steps.
Anyway, I do think any talk of changing the parenting agreement is really way way premature. It might make your wife feel better to discuss it, or even your Daughter but it perhaps should not even be on the radar at this point, it's so very cart before the horse as to be magical thinking.
I think it's so great that you and your Daughter are both in therapy. Never forget why you and she are there. This didn't stop the day your wife took off, this is ongoing and in many ways as bad as it was (for both of you).