I'm aware of your plan. She will still be in the cage for 14-16 hours a day if everything goes to your plan. That is a LONG time to not be able to stretch out.
Average wingspan for a cape is 25 inches/ 63.5 cm. If you have a cage that is 63.5x63.5 and she stands in the middle she will be able to stretch - provided there are no toys in the way. Minimum cage size is supposed to be 1.5x the width of your bird's wingspan and just as deep, which would be 95cm x 63.5cm
As I have said, my Jardine's is in a cage that is just big enough for him and he is out of the cage from 7am to 8pm everyday, sometimes longer. He was kept in a cage that was far smaller for 19 years and now barely flies.