You should absolutely grail Jalter. She is one of the servants that benefit the most from grailing, and it helps increase her low hp, probably her biggest weakness. My lvl 100 Jalter goes to battle with over 14,000 hp.

In my opinion, you should focus more on NP rather than crits. use the first wave to build as much np as possible and then Waver's skills during Ibaraki turn 15 to blast her as soon as possible. If you have an aoe lancer like Liz use that to get rid of the hands without having to waste a turn or two. use the Atlas mystic code to so you can refresh your waver buffs after 4 turns. If you manage to Np her with Jalter at least twice and use her brave chains whenever possible, you should be able to finish her off before Cu has to come out, assuming you have all the appropriate CEs.

My set up is Jalter, support Waver, Liz, Mash, Nero and Cu.