Just stick to using Kerry until either RNG blesses you with a better Valk from the gacha, we actually get the loli Valk that hits way above her pay-grade, or one of the better Valk event units shows up (star event for the plat Meirin, item collection event for the black Reshia).

NutakuDev has stated they want to get the loli in, and who knows maybe the JP devs will include her in the second map, in which case she unofficially becomes the real event unit while Emilia cements her place as a tin can replacement / Marribel skill up fodder.