Hi, I'd like to help you with your question.
Doing too much for your children and shielding them from hardships is a very common problem with parents today. Parents can feel guilty, protective or controlling when they run their children's lives such as your friend's wife does.
Although it is difficult to understand her motivation for this behavior without talking with her directly, there are some possibilities. One, she feels guilty about her relationship with their father. They could have fought a lot, there may have been abuse, or possibly affairs for example. The divorce could also be part of the guilt. So she tries to make up for any hardship by enabling the children.
Two, she is protective. She is afraid to allow the children to experience any hardships and so she shields them and does everything for them, so they never have to experience negative feelings, at least as much as she can control it.
Three, she is controlling. She may feel that she knows best and wants the kids to be in line with what she wants. If this is the cause, you may see other evidence of it with how she cleans her home, personal hygiene and her personality. Some people use control as a way to feel less anxious so controlling themselves and those around them make them feel ordered and less anxious.
Either way, this situation is going to cause problems in your friend's relationship unless they both are willing to compromise. If they cannot do this on their own it may be a good idea to have someone neutral, like a counselor or pastor, help them negotiate a better situation so they both feel they can contribute to the children's well being.
I hope this has helped you,