I'd be concerned about killing plant if I were to cut it back.
Down here peonies get mulched every year with zero issues.
Frost doesn't seem like it should have had any effects either.
Raking away the chemical residue from the fertilizer / herbicide (if possible) does sound like a good idea....
Any chems still on the mulch definitely should be removed.
How close to the plant is the turf?
Probably a good time to remove turf away from the flowers.
