I both love and hate it.
In a bubble it's awful. Hush is pretty bad, but at least has a little bite to the sound (harsh 'Hu' start), but adding the 's' makes me think of being told off by a cranky librarian. It's not cool and doesn't have any punch as a word (or onomatopoeia).
However, it's a female version of Hush. She-Hush. Shush. That's comic book nonsense at its finest.
I hope she has a better time of it than Hush, man was that character a damp squib.