No. She's not the same person. They're not sisters. The only relation
between them that the entire collective knowledge of alt.tv.mwc and
alt.fan.christina-applegate has ever discovered is that their names
sound alike.

Applegate is an uncommon surname but hardly unique, for instance,
columnist Liz Applegate.

Christina has no full siblings. She has a half-sister and half-brother,
both of whom are emphatically not dead porn stars.