Try just some ice-cream and anything else she likes which will give her some calories if not 'nutrition'? Especially if she is actually hungry--that's a good sign!!
MIGHT be the way forward?
Dad just didn't get hungry, so finding him something to eat and trying to tempt him could turn into a battle.
I still swear by the Oragel Max if my mouth's in pain, but I need to eat--10 mins before eating on pain areas, and I can manage it!
Brenda