The diarrhoea is a nightmare, but it will pass quite quickly you’ll notice, within 24/48 hours.
with my son I put a pad in his underpants to help, if she’ll allow this.
Also i went with toast cut up small and scrambled eggs no milk or a fried egg, mainly yolk and that helped.
piriton liquid for the itching if that helps, it’s a in the same flavour as minty toothpaste so maybe tolerable.
calamine lotion comes in a pink cream or a water bottle version from the chemist and that can be slathered on, the watery lotion with cotton wool dries like a paint so it’s not sticky like a cream on your skin for sensory.
if no cotton wool I used to just pour it into my hands and rub it on the body quickly , less fuss and done.
white bread dipped in chicken soup helped my son to bulk him up.
sips of bottled water helped , easier to sip from a bottle as opposed to cup plus I could see how much he drank.
calpol and ibuprofen helped.
I know it’s not a solution now, but if your daughters had it before , you can get the chicken pox vaccine if you have any sedations coming up.