If a healer is paid to work as a guard and their only way to contribute is to heal injured team mates, why would she demand extra payment?
The other members should then demand payment for protecting the healer if that's how she's going to play it.
This is giving me PTSD from running dungeons with awful party members in MMO's. Pretty sure I've dealt with this exact situation, on multiple occasions.
On the other hand I recall a very satisfying conclusion to one of those situations where the healer threw a bitchfit over something and refused to continue without compensation (party wipe or something), I just told the tank to keep going and took over the healers job.
Turns out the healer was probably at fault for the wipe because I could keep the group alive with time to spare for offense without even playing a dedicated healer build.