I work in growth marketing, focusing on ROI+ growth for a wide range of businesses. From tiny ecomm stores and pre-seed startups to 7 figure+ MRR, paid ads are by far a better bet than any type of podcast, influencer marketing, or more traditional TV/magazine/etc. Even just a few hundred spent on Facebook and Instagram ads will go so much farther than the type of podcast or influencer partnership you could get for the same amount, and that is of course amplified as your budget increases.
Podcasts & influencer marketing CAN work really well as a supplement to paid ads on Meta, Google, etc, but they tend to be much spikier channels - ie, to get one really good result you need to try 10, in hopes that that one will cover the cost of the 9 that didn’t work out.
The good news is horse products are of course niche and expensive, which is a fantastic sweet spot for paid social ads, especially at lower budgets. It’s actually much easier for the algorithm to identify potential buyers for something so narrow than for something with a huge market like, say, skincare.
Feel free to PM me - I love thinking about this stuff, and I’m happy to talk to your friend and give her some more specific ideas!