My own husband would never go on holiday, or if we did it was self catering like you - but that wasn't much of a holiday for me - he didn't have the excuse of being coeliac, he just doesn;t like holidays and never will.
He was happy for me to stay at home, looking at holiday brochures
Now I holiday alone, but I've missed out on so many places I'd like to see and things I would have liked to have done. I am 80 this year and have to accept I will never treck to see machu Pichu or be able to stand the heat of India or undertake the long haul to NZ or walk the pyrenees on pilgramage.. And there aren't many insurance companies will take me on either because of my age.
He acknowledges he has been selfish, but I can't put the clock back, and although I say nothing I grieve for the exotic places I've missed.
I am the coeliac here and in 15 years of travelling have never been glutened abroad.
If you really can;t face it - let her go alone or with a friend.