In the Age of Apocalypse, Sister Carlysle, aka Copycat was a member of the Brotherhood of Chaos, a group of mutant fanatics serving Apocalypse. When the Brotherhood received word of the Human High Council's air-lift -- escorting hundreds of humans from America to be transported to the still human-run Eurasia -- they arranged for Box and Copycat to board the transport undercover. Unfortunately, after arriving at the landing site in Eurasia, they were discovered and killed by Weapon X and Jean Grey.
In Age of X, Copycat was a traitor to the mutant race working for the Human Coalition. She infiltrated Cannonball's X-Force unit prior to the formation of Fortress X. Vanessa made intelligence reports back to Henry Peter Gyrich before being uncovered and apparently killed by Husk.
When Arcadia DeVille accidentally opened up a dimensional rift with overlapping timelines, [X-Force (1st series) #100] Warpath briefly met an X-Force version that counted both Deadpool and Copycat among their line-up. Although the details regarding their memberships were left unrevealed, there stands reason to believe that this Copycat had impersonated Domino too. After all, she was wearing a similar blue and purple costume. Possibly she was inducted into X-Force after she came clean about her working for Tolliver. The real Domino was not shown to be among that X-Force line-up, though, and Cable had apparently perished in battle against the M.L.F.