Lilias is very pretty, and I think it'd be perfectly nice for a girl of any age.
Lilias Mara is fine, but I wish I could sell you on
Lilias Mary. That's a combo that couldn't possibly be improved upon, in my mind. It just brings to mind all the best aspects of the romanticized image of Scotland, for me--the lovely highland lass in a field of heather, auburn hair and all. But I'm a hopelessly romantic American, so what can one expect? ;)
Other ideas:
Lilias MariaLilias Maren (MAHR-en, not MARE-in)
Lilias Maura,
Lilias MoiraLilias MarianLilias Marla
Array