I might not have even close to the same level of experience watching Star Trek as everyone else, but I think you can’t go wrong with starting her on on TNG. My dad started me on TNG, and I’ve been a huge fan of it ever since. It’s perfect for a new fan, since the show still makes sense even without watching the other series (though he has also shown me some of the original movies). And it lacks a lot of the sexism present in the OG series, which can be a turn off.
Though I found the first episode a little boring, it quickly got awesome as it went on. I’ve only watched that show and Discovery, but I’m pretty sure it will stay my favorite. The characters are likeable, Picard’s a strong leader, and Data is a great foil for the rest of the cast.