In the book that was published in advance of her 18th birthday she described how she was looking forward to the full student experience. So, I don't think it is her family pushing her but Amalia truly wanting something of that experience she had been looking forward to for a long time (and I assume several of her friends/housemates have been members for 2 years by now). Given that she is already in her third year, it must be even weirder to be part of the initiation rites carried out by students that might be in their second year, so in terms of student life her junior but in membership her senior.
Edit: looked it up.
In Dutch:
En gaat ze haar studententijd dan, zoals de familietraditie betaamt, doorbrengen in Leiden? Lid worden van het corps, zich aansluiten bij Minerva?
Niet als gegeven, zegt Amalia stellig. Áls ze naar Leiden gaat, en áls ze bij Minerva gaat, dan is het 'omdat ik dat echt zelf wil en niet om de traditie'.
(...)
Ze will sowieso in Nederland haar bachelor doen, en wil dan ook bij eht corps, met een jaarclub, alles erop en eraan. (p. 80)
Translated to English:
And will she spend her student days in Leiden, as befits family tradition? Become a member of the corps, join Minerva?
Not a given, says Amalia firmly. If she goes to Leiden, and if she joins Minerva, it will be 'because I really want to and not because of tradition'.
(...)
She definitely wants to do her bachelor's degree in the Netherlands, and she also wants to join the corps, with a year club, everything that entails.
At that point her intention was to do her Master's abroad - but now she had to do part of her Bachelor abroad due to unforeseen circumstances, so it will be interesting to see what path she chooses after her Bachelor.