I do feel it's up to Justine. If she keeps her game up, it should be over in two set. However, if she serves shits and makes tons of errors AND Mary gets all her guns out, Mary stands a chance for a 3-setter....then anything can happen.
One thing though, imo, Justine will not have to go for as much and in theory should make less UE. The normal left and right and occasional dropshots should disrupt Mary's rhythms.