Can these things be that private? If they turn you on wouldn't you want to tell your partner? I am very open about sex. But my wife isn't. She will let me know when she is in the mood, and she goes with the flow usually, but she won't talk to me about these things!
She is probably just shy or embarrassed about them, she doesn't want you to think she is a freak. Maybe start out slowly, with little things. Like telling her to tell you what to do to her. Like when you go down on her, have her tell you how she wants it. Start out slow with little things. Try telling her your fantasies and try to get feedback on them. Ask her if she would like that, what she thinks about it. It will take time but she will slowly open up. Don't pry and beg. Take it slow and get her comfy with it.
Get her hammered. Sounds mean, but seriously...you're married, so it not like you're taking advantage of her or anything. Feed her some cocktails, some compliments, take her somewhere fun...then take her home once she's all drunk and frisky and uninhibited...maybe she'll open up.
That's a really good question! It took me a long time to tell my husband what I was truly wanting from him. She may just be feeling embarrassed because some fantasies can be considered very taboo. She could have been raised in an environment where you don't talk about things like that. She may also be afraid that if she reveals these things to you that she could in someway offend you (if perhaps her fantasy does not involve you?) or upset you or turn you off. There could be so many reasons why she doesn't reveal these to you. Give it time and initiate these conversations gradually and make sure it's a give and take...she tells you something...you tell her something.
Lead by example. Some people will keep their fantasies quiet for a very, very long time because they're afraid that their partner will freak out and the relationship will explode. The greater misfortune is that because the fantasy would have been a deal breaker earlier in the relationship, she might despair of ever having that particular need satisfied. (This is why the serious sex talk has to happen well before the wedding.)
Decide, then, how you would handle a deal breaker. Power through? Let her meet her needs elsewhere? Divorce her? Figure it out, just in case your lady likes guy-on-guy torture scenes, while that happens to be not quite your thing.