yes, good idea for her to go to the A&E.
if she is not passing much fluid or urine, she could be very very dehydrated from her vomitting and diarrhea.
she most likely will need IV fluids
she could have a bad viral infection or influenza flu infection.
she might need antiviral medication like tamiflu to help decrease her length of infection.
the rash can come from bad viral infections.
there are blood tests to check for influenza infection.
I hope she feels better soon
let me know if you have other questions.