Best to talk to her and let her know what's going through. Because if you are kind of thinking of negative thoughts, the best thing to do is to let someone else know about it. The fear is always going to be there at first, and it's something to overcome... but it's always better to get support than to not have support.
You might find it better if you tell her the truth, but slowly let her know about things so that she eventually gets the whole picture.. that might make telling her about the matter at hand less daunting when you talk about it piece by piece. However, the feeling of release you get from letting out all of your worries at once is good, too. Also, perhaps you could talk to her and try to arrange a time when no one is around to have a good, private chat. That might make it easier for you to open up.
Most of all, just remember that your safety is the most important topic
Always be comfortable, and don't doubt yourself. Every step you take to help yourself is a step in the right direction!
Most of all, I'm here for you too!