This isn't like this is a religious celebration for you so There's no pressure to attend services or ceremonies that may be uncomfortabke for her, is there?
It sounds like you just want these days to be like a vacation and do some special activities that may cost money, including giving her a gift.
Is this the real objection for her?
It’s great that you are asking for the opinion of others. It might be helpful to know what country you live in since different countries have different holiday traditions. I think you need to ask yourself some questions. Why is Christmas important to you? Is it important because of your Christian beliefs, or is it important because of the holiday traditions that you grew up with? Once you have decided on your answer, you need to share it with your fiancé. If the answer is your beliefs, you need to explain to her what you believe and why you believe it. You are quite supportive of her beliefs, maybe she would be the same for you and your beliefs. It seems you have tried to include her in your Christmas traditions, yet she finds them silly. As a couple, you could make new traditions. Include her in the planning of things to do during your vacation times. You do not have to do what the rest of the world is doing. You can do what is comfortable and natural for you and your fiancé. It also sounds as if she doesn’t want to spend money frivolously. Maybe you and she could come up with things to do that are fun, yet don’t cost a lot. This sounds important to you. Take time to think about it, talk about it, and try some new things in December!