I had a similar situation, but I married the one with money.
You could tell her about it without giving an amount. I don't think it's dishonest to downplay the total. My wife make it seem like it wouldn't be that much, and it ended up being wayy more than I thought.
For example, when the time comes to talk about buying a house you could say you have some money in savings that could go towards a down payment. How you tell her about the money without giving an amount will depend on you and your relationship. For us, she didn't truly know how much she was getting, so she just said we should plan on having none. That way, I knew about the possibility but didn't include it in my financial planning. When I asked if she had a ballpark range she told me yes, but she didn't want to say in case she was wrong or the situation changed. She didn't want to say we were getting a certain amount, and then have our plans ruined if we got less for some reason. I didn't get the exact amount until we were married for two years and bought our first house. Ideally, you won't be dependant on that money anyway so it won't affect your day to day expenses.
Obviously your situation is different because you have a specific dollar amount with immediate access. I'd definitely make sure when you bring it up, you're sure you are getting married (or buying a house etc). You can avoid being seen as the "rich kid" if the money is brought up as "our" money, rather than just yours. And I wouldn't suggest doing that until you're ready to share finances. However, since it was left to you, I think you should decide what it will go towards before telling her. It's was a fine line for us because although we were married and I was involved in how it was spent, I realized it was given to her by her parents. She said it should go towards a house, but which house and where was decided by both of us.
I hope that makes sense. I realized I may have rambled. I can clarify anything if needed.