Well I haven't used Froslass all that much but I can tell you, if you want to use her as hazard set up, then you'd better use Focus Sash + Destiny Bond, so that you can get one spikes in /2 if they switch, then because of Froslass' average speed you should be able to pull off Destiny Bond if you're at 1 HP.
Froslass@Focus Sash
EVs: 252 Spd, 252 Sp A, 4 HP
Nature: Timid
Ability: Cursed Body
-Ice Beam
-Shadow Ball
-spikes
-Destiny Bond