I use a nearly identical set up (except I tank "SkullGreymon"(lol) w/ AW Rowanna) I gank the pumpkin king w/ Aw 39 Sherry and to survive and kill him all she needs is Eterna's skill activated and a healer (CC60 Fedora for me) replacing monica. I activate monica's skill to help kill the last enemies on her side before I withdraw her.
Draco usually gets a hit on Sherry before I get fedora placed but she always survives, and I don't have Iris (CC60) placed before he engages Rowanna in hand-to-hand.(the first time I did and 3* it but every time after he killed her before switching to melee, not sure why? So now I wait to place her and I don't think I even need her really?)
Point is if you place sherry ON Pumpkin king, not before and activate Eterna's skill she should survive (with help from your AW Iris and/or maybe Chydis w/ her ability active and/or any healer replacing monica). Also activate Sherry skill asap to kill a little quicker.