To add, she's considered an adult at 50, so 30-50 are the equivalent of human teenage years. So for all intents and purposes, she is still a child, about to become a teenager. Also, years lived is an extremely poor measurement of maturity, otherwise we would consider dogs and cats as having never reached adulthood.She literally said elves will rapidly mature physically at 30.
So in 4 years she'll physically grow older, unless the author has Dion pull another Deus ex Healing.
Though if you want to get really into it, even if she physically changes to an adult at 30, to elves she's still a child, but humans see her as an adult, and consider her as an adult since she would be 30 years old.
As for mentally, it really depends on whether or not elven brains mature at the same rate as humans. If elven brains don't reach mental maturity until the body is mature, then there's no legal loli here. If the brain is fully mature before the body starts maturing, a legal loli can then exist. Of course, I doubt the author actually thought that far given how shoddy the story has been.