She first played the character in 2003's "Daredevil" with Ben Affleck, then later in her own spin-off, 2005's "Elektra."
"Deadpool 3" is currently in production. No word if Jennifer's Elektra will have a major role or just a cameo.
Her involvement adds to the rumor that the plot will include a multiverse. If that's true, there could be more Fox Marvel characters (besides Hugh Jackman as Wolverine) since Disney now owns the rights.