So, I'm going to shill for Combat a little.
Also improves her rate of growth overall, making it feasible for Aeira to keep up with Hunger if properly supported and invested in.
It would be really good to have another party member that can keep up with Hunger. I've heard people say they don't want to invest in another party member, however, consider this: a lot of the thread want to take Ennobling anyway, and a lot of the thread have expressed interest in Philosopher's Wreath. Just those two things, which we're not even taking specifically for Aeira, would represent a lot of increased power thrown her way. On top of the +Progression from Combat, that's enough to likely keep her relevant for a while.
This ensures our little magic ninja can, in fact, stay useful for the short-medium term. If we go into Pillars of Creation or Total Eclipse, or pick up something like Gardener's Hallow or Azure Moon, we can add further buffs on top of that.
The point is, investing in Aeira is not very onerous, requiring only Arete expenditures that we'd pick up anyway for different reasons. Heck, once we win the Temple we're getting free upgraded Ennobling no matter what. She's not an Arete sink, she just puts increased priority on Philosopher's Wreath and other picks that have some ally benefits.
And having another party member, who can keep up with Hunger and be useful, is very valuable. Some people have been wanting to take Stealth focus because that's literally her job - but she won't be able to do her job for long if she can't keep up with the relentlessly escalating pace of Hunger's adventures. Stealth makes her better at her job now, worse at it later. Now, if you just want to ditch her at some point, then Stealth is definitely the vote for you.
Business is a weird one, because it changes Aeira's role from "Adventuring Party member" to "stay-at-home supporter." That's a different calculus, if she's not going to go on adventures she doesn't need to scale very badly. Business is the pick for people who want to keep Aeira around, but don't want to invest in her or care more about her role as Letrizia's friend then her role as a scout/assassin.