In this situation you are going to have to bring it up, basically say it in a way where she thinks you don't care either way. But umm, basically talk to her about your feelings for one another and make sure that you kinda towards the end of the conversation, say "I don't care either way, but i was wondering about how YOU felt about bringing our relationship to the next level". Kinda make it sound like you want her imput. The whole point of having a lengthly conversation about how you feel about each other is to set the mood, and to get her to feel loved and important, so that when you pop the question up, she will be more likely to respond in a more positive manner. It sucks, but in a relationship, both the male and the female need to think that their feelings don't matter and they only want the best for their partner. Because that way, your relationship will end up being a more honest one.
Remember say,"I don't care either way, but i was wondering about how you felt about bringing our relationship to the next level". Seriously try to make it sound like you would like to but don't care too much, and you were wondering how she felt about it. This way your not asking her for sex, your just invoking thought, thought that may very well lead to sex. Hope I helped man.