When your child is ill in hospital with infection, manic, there is no 'balancing' needs, especially not for a holiday. That ill child becomes the focus until such time as they're better.
The 'much loved sibling' is an adult who doesn't 'have no one', he has a fiancee, friends, etc.
' There are many circumstances which would make it impossible for both parents to be there. What if one parent was working away? Or had a contagious illness? An ill child needs to feel safe and loved. Surely one parent can fulfil those needs for a few days? It's pretty bad news for all of us single parents if not! '
None of that applies here, including the single parent thing, the OP is not a single parent. It's a wedding, not a court summons. This is not 'a few days', it takes over 24 hours just to get there. Seriously ill children want everyone round them if possible. Mine certainly did, and all the other children on the unit. They need that whenever possible. this child doesn't have a nasty cold, but is in hospital with a virus. So you're saying if you were the OP, you'd really be okay with being the one to leave your daughter in hospital if she had 'another parent' to look after her? Really? Yeah, right.