Hi Lee… I think it very much depends on the beta reader. Mine has a degree in Eng Lit so by definition is widely read, so I don’t think it matters as much. But (and this is just my personal opinion) if the beta reader’s dominant qualification is that they are a reader I’d say yes, they need to be familiar with, and a fan of, the genre you write because then they have a good idea of what a potential reader is going to want and expect eg a happy ending, an emotional journey, and also of what the current market (ie publishers) are looking for in the genre.
It is good that you can see how this might have impacted on her feedback – like I say, you need to know when to not accept certain criticism…
Thanks for reading 🙂 And best of luck, Lee! Sam