From The TimeSplitters Wiki

Mary-Beth Casey
Unlocked by	Complete Story Mode up to Planet X
Species	Human
Size	Normal
Accuracy	N/A
Agility	N/A
Stamina	N/A
Fire Proof	N/A
Shock Proof	N/A
Default AI	N/A
Native TimeZone	1965
First Appearance	TS1 Story Mode
Relations	Jo-Beth Casey (Sister)
Games	TS1

Mary-Beth Casey, much like her younger sister travels into a Mansion to fight zombies. She aids Peekaboo Jones in 1965 to relieve the Mansion's curse.

TS1 Gesture	Jumps up in the air, claps then stands still.	TSFP Gesture	N/A
TS2 Gallery	N/A	TSFP Gallery	N/A