Nandinas are native to eastern Asia. It does appear they have become invasive in the southern states. I have 2-3 growing in my Pacific NW yard with no sign of invasiveness, so I assume it is a regional issue. The level of toxicity also appears to be questionable - some birds may be succesptible while others are not. I have no qualm about keeping these beautiful shrubs.

With your window height, I would go with the Dwarf Nadinas. I have the regular ones and they come up to the height of my window bottoms which look higher than yours. I love my Nadinas in all seasons; they are mostly none maintenance. I do occasionally get 'volunteers', but they are so easy to puck up and transplant. I have even planted them in containers for height. Happy diggin"!