I would suggest that you and your mom take your dogs out for a long walk together. Neither of you should be over excited about meeting each other, stay calm and neutral. You can gradually let them smell each other, hopefully by the end of the walk some of their energy will be gone and they will be calm around each other.
Our trainer would not let the dogs meet or play either. As she got older, I realized she needed some social skills, we like to take her everywhere we can. I found a fun social group for German Shepherd owners. Being around her own kind has worked wonders. Now she can play with any breed. The website for the group is at meetup.com. I don't know if you have meetup groups in Belgium, but it might be something to look into.