She is recruitable at the house below the hills granting access to Leonid's Castle.
Gloria is very, very similar to Ruby, with high Strength for a mage(18), and very high Speed(23), making her a nice addition for a battlemage swordswoman.
Her Esper Magic is quite useful, as you can learn Fast Delta quite early and it racks some nice 2000 damage with low Custom Magic Level.
She is also a good candidate for the Arcana Tarot, since she is really fast and has decent Magic(20). Her Life Cane will prove her as a good asset for your party.