Age thingy, sorta

[Belcarl]

Each level of nature gives you +50 years of max age (before you get the aging effect).

Very few spells use a nature level higher then 4. But some gets better effects for each extra level. So generally, nature above lvl 5 is rarely needed, and most likely not worth the gem cost. Especially not if you are using empowerment to raise her level.

What kind of plans do you have for her? if you raise her air magic she could be a really good battlemage. Check out the evocation tree. Spells like Thunderstrike and Orb of lightning are very good with a high Air magic skill.