Sorry to be negative, but I think the whole Twilight craze (while dying) is still leaving its mark on Bella and Isabella.
It's a very pretty name but I'd be a bit wary of it because it (or more specifically Isabella with the nickname Bella) is so hyper popular that it may feel rather trendy and ultimately be generationally dated when the fad dies down.
I liked Isabella pre-twilight, but have put it aside for that reason...but maybe I care too much about what others think. BUT if you love the name and could care less if it's super trendy, more power to you, and go for it!