In the 'gf forced my mom story' situation, it's important to approach it with respect and empathy. The son/daughter who is in the middle should act as a mediator. They can start by having separate conversations with the girlfriend and the mom to understand each side's perspective. Then, they can bring them together for a group discussion. If the forcing behavior is unacceptable, the son/daughter should firmly but gently tell the girlfriend that this isn't the right way. And the mom should also be open - minded to some extent if the girlfriend has good intentions. It's all about finding a balance in the relationship.
First, communication is key. Everyone involved should sit down and talk calmly about their feelings and concerns. The girlfriend should understand that she can't force her will on the mom. The mom should also express her boundaries clearly. If it's a minor issue, a compromise might be found, like finding a middle ground for a decision. For example, if it's about a party at home, they can discuss and plan it together so that both are satisfied.