Isabella can at least shorten to
Isabel as well as the overused
Bella. Like
Rose, a
Lily is a
Lily is a
Lily! Also,
Lily comes and goes in the charts, while
Isabel seems to have more staying power.
If for some reason - like, I had a baby girl in the kind of country that insists on people using names from its official naming list only - I had to use
Isabella, I'd use
Isabel all the time, without a nn.