It's a really small world of magic if she holds 10 of the 12 (or 13) strongest summonable spirits. Makes me want to think they aren't the strongest things an accomplished celestial wizard can summon. It would be ridiculous. Just as ridiculous that she (and her late mom) would be the only celestial mages who aren't/weren't complete scumbags and thus all the spirits would like to work for her. Perhaps Mashima himself realises this before long and introduces a non-celestial summoner. Like some demon summoner.