Hi Phil, welcome!
That's a very interesting and complex question... one that often comes up from friends / family of people choosing a BDSM lifestyle or frankly indulging in various other fetishes.
I think the answer is that there's no real way to know for sure...
Fact is, all fetishes do have their roots somewhere - and it's not always the obvious one. If you spend enough time and money, you'll probably track them down somewhere. Maybe in childhood, maybe in a genetic disposition, who knows. It is however a slippery slope to start diagnosing where different fetishes come from, and can lead to a lot of heartache.
The big question is... does this situation pose a problem for her today?
Is she in a relationship with someone that is harming her, holding her against her will, etc. Is she being physically or emotionally abused?
Or is she making a lifestyle choice that concerns you - as her friend who is concerned for her, yet someone who does not approve of that type of lifestyle.
Contrary to the outward perception for people not truly into the BDSM lifestyle, BDSM is not (in general) about emotionally "abuse" relationships. Those relationships are in many cases very loving and nurturing. Of course there are dangerous, sadistic people out there, and society needs to protect itself from them. So it's a matter of being truly informed of what's really going on.
And another big question - is she seeking your help, or do you feel that her choice to partake in BDSM is obviously related to her childhood so she should choose to stop doing it?
Your concern for your friend is admirable, just beware of trying to fix someone else's problems they way you feel they should be fixed, as that can easily end a friendship.
We all have to live our lives, make our choices every day, and make our own "mistakes" (though what seems to someone as a mistake can be just a life experience to someone else), etc. Please don't take my comments in any negative way, just layout out some thoughts for you to consider.
Also, check out these related videos for some related thoughts...
Are Sexual Fetishes Bad? How About Kinky Sexual Fantasies?
BDSM Delimma - Should I Tell My Parents?
Can a Virgin be into BDSM?
Thoughts?
Dan