It sounds like you're handling it just like you would if she was your biological daughter (and as a VERY good mother would!), which is exactly what you should do, in my opinion. The only down side to the situation is that she isn't there all the time so you'll have to assume a lot of the responsibility. But really, if you have a 16 year old with a cat, who's going to take care of it when Jr. goes off to college? It's not really much different.