Well,
Allie is pretty short so I'd rather see it as a nn. But I think it could stand alright on it's own. I myself would use
Alexandra (or
Allison,
Alicia,
Angelina... some A name) so she had another option when she got older if she didn't like
Allie or thought it was too childish. BUT that's just me, I'm not big on nn names in general... with a few exceptions like
Kate. For the most part I think
Allie would be fine on it's own. I do prefer spellings
Ally and Alley though. It's a cute name and I like it.