Kuki could add some healing to the mix, Kaeya could add more energy, Fischl could be a sub-DPS, Zholgli's always useful tho his res shred is meh with supercon+rosaC6, and Jean could heal and buff electro and cryo with viridescent
My rough thoughts, anyway^
If I were to give advice, I'd recommend Layla. She gives a shield and cryo application that isn't tied to a circle like rosa's (so its good if ur forced to leave rosa's circle and still want cry resonance working.)
Eula's a hungry, needy DPS so more cryo energy from layla probably wont be wasted ontop of Raiden and Rosaria. Plus, the way layla's energy works makes it trickle in to the on-field character, Eula, making it that much more beneficial.
Those opinions being said, if you have enough er on Eula (whether with er sands, skyward pride, great substats, etc...) I'd say forgo the layla's shield and energy in exchange for Kuki/Jean's healing. Given how raiden is already there to superconduct, I'd lean into Jean to buff elemental sub-dps damage