She can be recruited at any time by talking to her in Neverwinter's Temple of Waukeen. To enlist her, the player must pay a one-time fee of 5000 gold (can be reduced to 3000 gold with a bluff or diplomacy check).
Belueth's stats are very good thanks to her unusually high Dexterity score: Str 12, Dex 22, Con 14, Int 14, Wis 10, Cha 10 at level 8 - normally impossible for an Aasimar, equivalent to pointbuy 40 assuming 20 dex at level 1 is worth 24 points. Her feats are acceptable: Dodge, Toughness, Weapon Focus (Shortsword). Overall, she can be a very useful companion.