First of all, little vocabulary nitpick: since Mark and you are not involved, this is called a Vee, not a triad, in which all three partners are involved. Laura's position is called the hinge, and Mark and you are considered arms or branches.
Typically, the best way to relieve pressure that's on a hinge is to make sure not all communication goes through them. The arms have to communicate directly and address issues directly, as well, and conversations involving everyone at once should also happen.
It doesn't seem to me that there is a problem of communication here, though, so I'm not sure exactly how to help. Do you have some more precisions about what stresses Laura out?