What level of detail is appropriate? Is she a stock broker or a finance person? Does she need to be convinced of its security model? 

To make it very simple, like for a 5 year old: "Bitcoin is like digital gold and if you have it, you protect it like you would protect jewelery or something you keep in a safe deposit box. Its better than bank money because you can protect it with only a secret, and like cash, no bank can stop you from sending it to someone. You can send it over the internet because its digital, but its even more scarce than gold, and its value is closely tied to the electricity it takes to produce it. Its the first, and eventually probably the only thing in cyberspace that is actually scarce. Its far more scarce than gold, but its also far more divisible than gold. As long as it continues to be adopted in place of inflatable money its average value can only ever go up over time."