Ash had yet to register as a Balancer since her identity was still an issue just like how it could create many problems for her in the ordinary world.
Perhaps she could find a way to register as a Balancer within a Balancer organization without a clear identity but that would still come with several rules and restrictions.
One of those restrictions was not being able to use the methods she had been using so far whether it was risking exposing her shapeshifting capabilities or gaining more power after killing Spirits or other humans.
If she was working with others then she would have to limit herself in many ways.
Either she would have to stop herself from using them and lose out on the potential gains or she would have to risk exposing her secrets as she still tried to seek out those gains each time.