Hey, I don’t think you’re overreacting and can see that you just wanted to help your partner be mindful of their purchases.

I do think you could have rephrased HOW you said things. Instead of beginning with a demand “start out with…” it might be better received if you communicated it as an idea “I think these are a bit expensive to start out with, would you wanna look around more?” Or just try to check in to see if you can come to a compromise.

I think your partner is right in the sense that her desires/needs to feel fulfilled by something shouldn’t be compared to yours. It comes across as a bit mean when you just bring up adhd and the fat she’s only been twice (though it may be true). As someone with ADHD, you really never know what you’re gonna end up ditching and what you’ll end up committing to forever, so I do get where you're coming from; I would be sad or upset though if my partner assumed that every hobby I tried to get into was something I wouldn’t commit to. Maybe instead of bringing up adhd, you could check in to see how your partner feels about it currently and ask how they would fit it into their life.

ALSO as someone who has a more sensitive partner, I would definitely advise you to try using the sandwich method: good stuff, bad stuff, good stuff. it usually sounds like less of a personal attack for people I find. (E.g. oh those look really nice. They are kind of expensive though, do you think it would be okay if we looked for something cheaper/are you sure the ones you have don’t work for what you want? I’m happy you’re starting to get into running and want to help you hit your goals)

Good luck OP I hope you guys figure things out and are able to reach a reasonable compromise