Post-Invasion Files:
Doctor Mossman was transferred from City to City by the Union, before finally arriving in City 17. When she heard that Doctor Wolfe was here, she made extreme effects to contact him. Finally, she got in contact with Joseph Deupree, who agreed to smuggle her out via the 'underground railroad' that fed through the canals. Both were nearly captured and killed in a night raid on one of the railway 'stations', but they managed to slip out and make it to Black Mesa East undetected.
From there on out Mossman worked with Doctor Wolfe on various projects that would boost the Resistance's chances against the Union. In particular, she re-instated her research on gravitational manipulation, eventually creating what became known as the 'zero-point energy manipulator', or gravity gun.