Sensitivity varies a lot from person to person, and some people that are pretty sensitive still won't reach orgasm that way. For others, myself included, it is possible and even pretty damn easy, and honestly fingers alone are plenty. Gentle flicking, grabbing at the whole breast, and circling the araeolae does the trick generally, but it's generally a full body experience for girls so stimulating her elsewhere (neck, torso, legs, etc) helps too. Vibrators don't work quite as well there for me, though they do still feel good. Nipple pumps are a good idea! My partner uses clamps and that also tends to make them pretty sensitive - could be an option depending on if she leans masochist at all.
Have fun!! Sounds like she's in for a good time 😁
I notice them but not frequently. They are a little sore sometimes, and if I carry something resting on my chest or walk into a doorway or something, that can hurt quite a lot. Occasionally they'll get in the way of positioning my upper arms, but they're not big enough for that to happen often. They can slip sometimes if I'm wearing a bra, so I have to readjust em for comfort sometimes. My nipples don't get very hard, but they're sensitive all the same and if I'm not wearing a bra the fabric sliding over them can feel really good. Annoyingly so, much of the time. But I enjoy having em - my chest stays pretty warm, it's pretty comfy to lay on my front, and I like what they do for my figure! The feeling of them being held in a comfortable bra feels nice, not really in a sexual way, but it's like a warm hug.