So, I explained that she is great at doing nice things for others, but MOST of the time it includes something for her, and a few times it doesn't. I told her that she needs to practice doing truly selfless things for others, in order to balance it out a bit more. I told her that a truly selfless act is one where you're giving to the other person, and you're getting nothing out of it for yourself.
She liked the idea and agreed that it was something she wanted to get better at.
Then last night, we were all watching a tv show together (Mork & Mindy - we're going through each episode right now, from the premiere right through) and she began scratching Mark's back. She did it for quite a while. Then, she surprised me by asking me to move a bit so that she could scratch my back next. After that, she didn't ask for a thing. She just sat and watched the rest of the show with us.
After the show, I gave her a big hug and told her that I was very proud of her and I asked her how it felt to do something selfless. She said it felt good.