Information needed

Once the becomes Belgian/EU you can immediately apply for F card provided she has a salary of more than 1600€ net/month.
But be careful. I wont recommend you to apply if your A Card has less than 6 month left in the moment you apply. The reason is it takes 6 month to get the F card approved. If meanwhile A card expires they will give you Orange card which is less inferior(Cannot leave and re enter Belgium on an Orange Card)
Also for applying for Belgian Nationally any period on an Orange Card will be considered as interruption in your case. So you would have to wait 5 more years