Yeah the money thing is a rather weak argument here I mainly brought it up to show how unlikely it is in my opinion. But on a more general basis it could be as clowns234 said, Gambling Debts, Drugs, falling for some Scam or something like that, but nothing of it would fit good with Lindas Personality in my eyes.
It would be interesting, indeed, but I can't see it really fitting with her actual Personality. Also i would find it much more compelling if the Video was just a quick flash of her more naughty side that she is ashamed of, and MC is "freeing" this side of her. The Mother Daughter dynamic could work here well. With Rebecca having "inherited" her Mothers naughty side but embracing it instead of being ashamed of it or something like that.
The Video also could be a result of an Affair of the Lonely and Sexually frustrated Linda, depending if the Video was a Professional or Amateur one, can't remember what it was. With the Affair ending after she regrets the Video and going back to being the brave (but unsatisfied, lonely) Houswife for the sake of her pretended "whole Family".