Translation:Her stepmother wanted her to bite into the apple.
Let's see what's happend in german: in einen Apfel beißen, means bite into an apple or take a bite out of it. Nach jdm/etw beißen means bite at sb./sth. I guess it is similar in dutch.
'......ze in de appel beet.' - does this mean that she is to take a bite from the apple (i.e. removing a piece), or, as implied by the English translation given, that she must just bite the apple without actually breaking off a piece of apple - like a child biting someone?