Weren't for Aerie's array of spells I'd have kicked her out of my party - low HPs and slow level progression are her weak spots indeed. Fortunately, I had a powerful mage in my party, Nalia (could have used Edwin but he's evil) and a powerful cleric, Anomen, to help her. Keeping her alive was a challenge, and NO, I never used her as a fighter. I used stoneskin and the girdle of fortitude all the time. Maybe it's because of her saving throws - the lowest the level, the worst the saving.
Aerie is very good at the beginning, but at later stages I needed more Heal spells and wanted to summon more skeleton warriors... too bad she couldn't reach level 15
... and more Abi Dalzim's Horrid Wiltings... I was extremely disappointed when I found out Aerie couldn't cast level 7 and 8 mage spells, plus she got level 7 cleric spells by the end of chapter 6. Despite this, I kept Aerie with me because I was near the end of the game, but I'm not sure I'll take her in my next adventure through BG2.