I have both of my nipples pierced. As well as my ears, eyebrow, tongue and navel.
The nipple piercings did hurt the most upon needle penetration, out of all of them, but literally only for a second. Once that was done and the jewelry was in, they didn't hurt again ever. At all. Easiest piercings I've ever had to heal as well.
I absolutely LOVE them. As (Foxy I think it was) stated, there are advantages in bioplast (plastic) jewelry, especially for the post (assuming a barbell). It is a much more comfortable and forgiving type of jewelry.
If your friend wants it, and is going as far as consulting with a piercer, she'll likely be very happy with them. If it's a whim thing, then I could see someone being "meh" about it, but when it occupies your thoughts, it's more than a fickle trendy thing.
I love the way mine look, the way they feel. They make me feel sexy, and I think they make breasts I already liked, look that much better in my eyes. I have extremely small jewelry, so in my case, the effect is very subtle, but I absolutely love it.
Oh, and the only thing I've caught them on since I got them is the occasional thread of my shower poof. Never hurt or caused damage.
It's a personal thing, but it sounds like your friend really wants them, so I think she should go for it!
I would have no issue posting a picture of mine, but I don't want to ruffle any feathers. LOL If you're curious to see or think your friend would benefit from an example different from the typical gaudy (IMO) hoops, PM me, and I'd have no problem sharing. Same type of pic you'd see in a piercer's portfolio.