It is an offer Heylian is more than happy to accept, and he promises whatever extra wares he gets out of his share of the loot she'll get first crack at.
In order to support the team most effectively, be it from a range or from melee, Heylian requests to be just before the rearguard. That way, if they are attacked from behind, he can help mount a defensive wall, and if they're attacked from the front, he can pepper them with bolts.