I'm very sorry to hear about your story. I wish you and the rest of your family the strength to get through. Sounds like she was an amazing person, and at least cared a lot about you guys. You always have that to remember about her, and I'm sure she's thankful about it. Just remember whenever you accomplish something, she's looking from somewhere, smiling, knowing, and proud about it.

As for the task at hand, I'm really not the best person to ask for advice. My suggestion would be to tell whomever you end up being with. You will feel much better if you tell that person, even if you end up crying (I'm sure you will- nothing wrong with it), just because you got it out. Whereas, if you just keep it a secret, you'll feel haunted in a way about it.