I used a workaround to solve the issue:
– I added a user with role “student” to the main site of the network, where the plugin settings are managed.
– As a consequence, the role “student” also showed up in the list of roles that the Support System plugin allowed me to assign permissions to use the features.
– Once the “student” role had permission to use the plugin, it also worked on the child blog of the network.
Problem solved, no need for you to dig into the code of the other plugin 🙂 But thanks for offering!