I read an article a couple of years back that said that adult cats might struggle to process the higher protein levels, and that can put a strain on their kidneys/liver, so it might be OK in the short term, but not in the long term. At 2yo, your ragdoll wont have stopped growing yet, she still has another year to mature, so I wouldnt overly worry. I have had lots of underweight cats (in fact, 3 out of the 4 in my house at the moment need to gain weight), but prefer to use things such as cat milk, extra dry, chicken, tuna, treats, an extra meal, a/d etc than kitten food.