Her main weakness is her extremely low df of 5.
The trick to LJ vs Rezzers is Restore Natural Order, Last Rites and her paired pistols.... YES her paired pistols. My local lads are absolutely baffled why I shoot with LJ rather than smash things up in melee. Because of RNO and LR, that leaves her with no AP to attack... that is why she has to be played defensively until the Rezzer player has no resources to try and win the war of attrition. Let the rest of the crew kill the Rezzer's minions and activate LJ last to blow up all the corpse tokens / deal final wounds with RNO.
Also, bring a Student of Conflict for LJ. It really makes her extremely dangerous.
Of all the Rezzer masters, McD (McMourning) is the hardest master vs LJ. He is a combat / DPS nightmare and is as fast as LJ. He starts with a bigger SS cache too that makes killing him in 1 activation nearly impossible.