I would say a normal (and IMO) sensible approach would be for her to have various engagements both solo and with her parents, domestically and internationally while studying. - For at least giving her some experience.
After all, when will her studies be completed? When she is 26 or so? In reality probably older.
So when the detractors come - and they will - saying: Where is Amalia?!? She really should blah-blah!! The answer will be: No apanage, no obligation. No pay, no work. That's what you wanted, wasn't it?
Personally I don't think Amalia should return her apanage. Nor do I think it's a good idea to bow to (some) public and political pressure regarding the apanage.
- Because Amalia is working!
She is currently an apprentice in the business called The Netherlands, on a life-time contract, learning the trade. And apprentices are usually paid.
Apprentices are long term investments, who in periods spend time at trade-school.
Giving in, which I believe is the case her, is at best a futile gesture, because the detractors will never be pleased. So stop trying to please them.
It boils down to: How do you measure the work of the royals?
The answer is: You can't.
Because there is no finite answer.
So giving in to public pressure will only encourage the detractors to demand more. - Lend the Devil a little-finger and he'll take the whole arm.