Welcome to the Wefugees Community and thank you for your question.
For a familiy reunification with a German citizen, it is not a requirement that the German person is working or having an income (even though it may simplify or speed up the whole procedure). Since you were giving a pre-approval letter (Vorabzustimmung) from the Ausländerbehörde already, I would not worry too much. Relevant are your German skills though, as you may prove skills on minimum level A1 - did you consider this?
All the best and looking forward to your reply,