iPhone is listening

Ok I have a question. I'm kinda a noob when it comes to privacy. I'll follow the guides and do the things to try to minimize ad companies selling my data etc.

Some basic stats: I have a Samsung running stock android. My GF has an iPhone. I use brave as my standard browser (I know that's not super popular but I haven't made the move to Firefox yet.) I have DNS level ad blocking on my router cause I hate ads with a passion. She uses safari.

So here's the deal. I was browsing the web looking for gift ideas for Christmas and came across some moccasins I liked. I mentioned to her that I liked them and browsed their website for a few minutes.

About 10 minutes after that, she's checking her Instagram and sees an ad for the exact brand of moccasin I just told her about. Just for kicks, she also checks her Facebook and sees the same ad there (makes sense cause it's the same company).

My question is basically how on earth did she get an ad for something I looked up? And how can we prevent that from happening? It's very very disconcerting to have ads pop up on others' phones right after looking that thing up.