That does help lay it out, but when I say 'billing agreement', I'm talking about a framework by which she could evaluate the charges. A formula or set of formulae, if you like, where if you know the time spent on the task, the charge rate and any extra charges based on circumstances, you can...
I'm posting this on behalf of a friend.
Basically, my friend has been concerned about how much her lawyer was charging her for his services while managing her estate fund, which later became her trust fund. The management was passed to him from her old lawyer, who died before she came of age...