If you're thinking long -term, assuming neither of you are Trust Funders, there must be some joint goals?
Eg: Are you planning for children? One of you may need a career break/want to retrain. What if one of you is made redundant.
When you say "no money worries" that's great, but then maybe you should look at putting some spare income towards early retirement, etc? With two good incomes, you can move towards this joint goal sooner.
If she's not on the property ladder, she's actually in quite a vulnerable position if she isn't saving income. Eg, does she have savings in case your relationship goes tits up and she is homeless?
At the moment, it looks a bit like she's just part of "your life that you've already made". Which is natural given the age gap and that you're further ahead in your career.
But I think that "lets talk about OUR joint financial goals" is a better stance than "right, start contributing". As in "what kind of life do we want, what are OUR financial goals, how can WE achieve them".
You're in the DINKY stage now (double income, no kids) which is traditionally the "easy part" financially, you need to start building a cushion.
At the moment, it looks like you're asking her to contribute to the life which you have already decided on?
Where does SHE want to go on holiday or spend her leisure time? Maybe if she was paying half, she'd want to go to more studenty, cheaper places rather than luxury breaks. And then you don't get to just pick what place looks nice for you. Are you willing to give up that control?
Once you are BOTH involved, then I think things will feel more equal. But I wonder if you've slipped into a bit of a "lover who does nice things" role with her and enjoy taking on the role of "I'm the adult who had 100% say on holidays" - she's the child/pet who is treated.
What you need to be moving the relationship towards is "equal partners"?