If I'm reading your question correctly, you said that you proposed on Face Book? If you did, no wonder she didn't answer yet. A marriage proposal is done face to face, not online.
I proposed("I love u ") to my crush on Facebook 3 months earlier. She didn't refuse but she just told me she doesn't have an answer till now. Whenever she have the answer she will let me know. It is embarrassing to ask her the same question again. What should I do?
You don't propose to a crush.
A proposal is a social and legal commitment for marriage. She is not giving you an answer because she is too young to know how to handle this situation and doesn't want to hurt your feelings. She is a crush, which is not the same as a long-term relationship with an equal.
Instead of proposing, ask her out on a date. Leave the proposing stuff alone for a few years neither of you are ready
This is not the kind of relationship that is ready for marriage. Sorry but not even close, couples need to spend time one on one getting to know each other in person. A few manage to do otherwise but a public online proposal is not what anyone wants. No answer tells me that the answer is NO but your feelings are trying to be spared. You are not being taken seriously. I understand thing may be different there but family may have other plans you aren't aware of.
Because she's shy and gentle, you do nothing. She knows how you feel because now you have told her. Keep continuing to talk to her as you normally do, but don't bring this up again. If she's as shy as you have made it seem, she needs time to think about what this means and she needs time to figure out how she feels about you. It sounds like she is a gentle spirit. If she loves you back, she will let you know. Just stand by and continue to be her friend. Good luck.
First of all, what on earth are you doing proposing on Facebook? A marriage is something that could last the rest of your life, so Facebook is the last place you should be doing that.
Secondly, leave her be. Don't pester for an answer or you're probably going to end up scaring her away (if she hasn't already been scared away)
If the answer was yes she would have told you already, she's trying not to embarrass you and to let you down easily. She keeps telling you she's not ready which means she doesn't want to get married now, you're both 17 and in school, how would you support a family?
I think you should leave her alone and look around for somebody else, if she changes her mind she'll let you know. If you keep asking her it will only make her feel that she was right not to accept you.