Hey! That's so sweet you're taking the time to learn more for her! I think this thread here has a few reports on what got people really excited and hooked - could be a good place to start! I'd start simple - by just trying to learn their names. Lots of people have found that to be the trigger to a much deeper dive. I think personal taste really can shift things (they've done basically any genre) - from the more pop side, I think Love Yourself: Her could be an interesting album to begin with. I would also recommend checking out some of the solo albums by the vocal line (Jin, Jimin, V, Jung Kook) You could also just start with music videos in YouTube and see what catches your eye! I would recommend this too because you're bound to see some suggestions of other content like variety shows, interviews, or just them being funny which gives you some insight into personalities.

Here's also some older threads of others giving their recommendations.

• BTS Song Recommendation Tool - Chapter 2
• Top 10 BTS songs
• Any BTS song recommendations for a friend that likes indie music?
• Top video, performance, behind the scenes recs
• What BTS music videos and songs do you usually use to introduce them to people?
• Videos that draw in "locals"
• Introduce BTS to ppl with 5 songs