First of all, it's wrong to "force a friend into submission." It's your friend's human right to do whatever the hell she wants, regardless of your opinion. Second, the answer to your question is right under your nose. If you know something about her that she doesn't want anyone else to know about, how else are you gonna force her to do what you want? Beat her with a banana? Obviously, you can use the knowledge you have of her. However, I'm not saying it's right to blackmail her with something. She's your FRIEND for Christ's sake. Why would you even want to force her into anything in the first place? As her FRIEND, why can't you just respect her decision? Are you really going to resort to blackmail? Because that's low. A true friend never tells anyone her friend's secrets. If you're a true friend, you wouldn't even consider "forcing her into submission." I'm just a bystander here. I don't know the whole story so I'm not gonna say more than this. However, I'm sorry but I can't say I'm not judging you. A lot of my "friends" betrayed me in the past years. I know how it feels to be forced into something through blackmail and it's not the best feeling in the world. Your friend trusts you enough to tell you her secret. I so hope that you respect her enough to keep her secret. That's the least you can do as her FRIEND. 
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thanks for the advice but this is not the answer . I need an answer that is related to the meaning of submission.