First off, I'm sorry she reacted that way, my mom is very much the same and its frustrating so I know where you're coming from.
I feel like I would find historical examples of why that's not true. Maybe information about the history and how common different relationship forms are around the world to dispute the fact that we must "pair up." For example there is a matriarchal community in southwest China called the Mosuo who have no concept of the nuclear family model or marriage and practice what's called a "walking marriage."
"Men and women practice what is known as a “walking marriage” – an elegant term for what are essentially furtive, nocturnal hook-ups with lovers known as “axia”. A man’s hat hung on the door handle of a woman’s quarters is a sign to other men not to enter. These range from one-night stands to regular encounters that deepen into exclusive, life-long partnerships – and may or may not end in pregnancy. But couples never live together, and no one says, “I do”.'
While scientific research isn't necessary to validate aromantic experiences or any other experiences that are negatively impacted by amatonormativity, I find that people who are closed minded to topics like this tend to require proof that not everyone is like them and that alternate ways of thinking and doing things are valid and functional. Hopefully responding this way will open them up to the idea that their beliefs aren't inherently correct just because that's what they've always done and been taught. That's the goal anyway! Good luck with your project though it sounds really interesting!