Should our teenagers help because it's right or to be paid?

My oldest daughter Danielle has always been very eager to help others in her life and has never hesitated to offer her assistance. She never seems to concern herself with whether or not she can, has time, or will be rewarded. She simply jumps in and picks up some weight. I have always admired this in her. Her willingness to help came into play a few months back when I was attending a class full of moms striving to learn more about themselves as parents. These women came from many different backgrounds and faced different challenges as parents.

As with all classes this one had a graduation day and one mom was nearing this time and excited to be. She was 9 months pregnant and thankful to be able to complete the class before the birth of her third child. Her two older ones were very young, 2 and 3 yrs and sat at home with a friend while mom attended these classes. For her last class a situation occurred causing her to not have a babysitter and her kids were too old to sit in the class and too young to be outside alone. She was out of ideas and afraid she would not be able to complete the class. I offered to have Danielle sit outside with her children while she completed the last class and the instructor gave the go ahead.

After class I came home and told Danielle of the upcoming class and what she would need to do. I didn't ask her to do it, I simply informed her that someone needed help and Danielle was able to provide and the expectation was that she would. Danielle has grown up with this expectation (all my kids have) and she has the same expectation of herself and went to the class and sat with those two little kids.

Afterward the instructor pulled me aside and asked if the other mom had paid Danielle and I said no. We weren't helping to be paid, we were helping because it was the right thing to do. The instructor didn't share this thinking and openly stated that Danielle SHOULD be paid for giving up her time for this mom. I was offended. Danielle tried to refuse the money and said that she didn't want to be paid but the instructor insisted. Danielle said later, "mom I didn't want to take the money but I also didn't want to be rude to her." She made the right choice, if people want to pay us for our help there is no wrong in receiving it, however I was offended at the instructors reaction.

She believed that it was not acceptable for my daughter to help someone just to help her. Has our culture really come to a point that our teenagers are no longer expected to be willing to help because it is right? Has anyone else had a similar situation with their teen? If so how did you handle the situation and what impact did it have?