[@KoL]

I think theres also the fact that she hovers out of the range of many NP's (that and she could probably fortify the hanging gardens against such attacks via the powerful magics she possesses, The only ones she couldn't defend against would be absouletes, E.g Ea or thinks that ignore magical defenses) 

Besides, The hanging gardens are large enough to take maybe 1 or two anti-fortress attacks head on and still float. What is important to note is we don't know if the hanging gardens require manual repair once the NP is active or if the gardens constantly regenerate.