At 5 stars she's pretty great. I use her in tandem with Garrick and they just wreck everything. The only issue I can see with her is that she puts herself in much more danger to do her damage. You don't want to use her if you're facing a Cara, for example. Nightshade's powerful hits will usually build Cara's ult quickly and she'll be the first target for it being right out in the open.
Server: 090 Spartan Dagger
Guild: Leader of AVALANCHE - 50579