What's missing from the question is the general competency level/English competency level of the OP's mother.

Assuming some English and a reasonable level of general competency, it makes much more sense to meet landside.

There is an official meeting point landside - https://www.schiphol.nl/en/facilities/meeting-point/

I would suggest Starbucks, but I think there is more than one landside so that could get confusing.