The disappearing settings/APN problem is a common one with some Samsung Galaxy phones (worldwide) and unfortunately I have never seen a solution - Samsung don't seem to help their customers fix it.
What make and model of phone is your partner's?
Even if you have been with 48 for 6 years internet abroad (in the EU on Guido membership) will only have worked since June last year - before that they never supported internet while roaming abroad.
You might want to contact 48 support for more advice here - see the link in my signature below.
Hope this helps.