Froslass has no boosting options outside of Double Team. Plus, most of her stats, barring speed, are fairly poor (80/80 offenses, and 70/70/70 defenses). I'd be inclined to say to drop her altogether if you're trying to use an offensive ghost, as her niche is the fact that she can set up Spikes with her high speed while simultaneously blocking Rapid Spin by virtue of her ghost typing. If you're not using her for that, she's outclassed by Gengar, who is equally fast but hits considerably harder.
I'd be inclined to say to swap her for Gengar, and supplement him with Mamoswine for your ice type needs. It offers you an electric immunity, and a potent STAB combo with the strongest Ice Shard in the game, and a massively hard-hitting Earthquake, which is ever valuable. Something along the lines of...
-Focus Miss Blast
-Will-o-Wisp/Whatever coverage move you want seriously Gengar's movepool is huge
-Rock Slide/Stone Edge
-Stealth Rock (a godsend for competitive, but not worth it in-game)
...But if you want to keep Froslass, then drop Ice Shard for Thunderbolt (she outspeeds most things weak to Ice anyway). Spikes is good competitively, but in-game, it's worthless... plus you'd have to chain breed to be able to get Spikes on it, so it's probably an ordeal. She doesn't have many other options offensively, so you could go with something like Destiny Bond or Thunder Wave for more utility.
And it goes without saying to forgo Mamoswine if you keep Froslass.