It's great to hear that you've matched with someone whose interests are so similar to yours, but I think you might be setting yourself up for failure if you're casting such a narrow net. You're highly unlikely to hit it off with any one match on a dating app. As other people on here have already said; it's a numbers game and it's hard enough as it is, so don't limit yourself to just vegans or communists. And if you match with a non-vegan or non-communist, for the love of god, don't talk about either of these (sorry)!

As to what to message her; refer to something in here photos or the text on her profile. If that doesn't work then whatever else but keep it simple and casual and let the conversation naturally go to more meaningful topics, don't force it. Finding the perfect message means less than you think, it mostly depends on whether she's into you and whether she's in the mood - things that are outside your immediate control.