With the Hexblade curse extended crit range advantage then gives an attack a 30 percent crit chance. Double advantage is pretty awesome for someone who will frequently get advantage. Also consider Elven Accuracy at some point. On the latter note she should go for a shortsword, so she has the offhand option. Sometimes you have to go ranged (and Eldritch Blast will eventually fall behind being able to use sneak attack) and sometimes you want to make an offhand attack. Pump Dex over Charisma in case she has to use something other than her pact weapon. This requires concentration (so no hex) and doesn't get to use pact weapon features, but it would be a 3d8 necrotic damage finesse weapon with auto advantage for sneak attack in dim light or darkness, that can be used for an offhand attack with your pact weapon, or can be used for a Booming Blade attack and that you can even throw a few feet if you really need to and then summon back.
At level 5 you'll be able to upcast Shadow Blade (a spell she should learn) to level 3 making it 3d8 instead of 2d8.
Many will tell you extra attack isn't worthwhile on a Rogue, but it is a second bite at the sneak attack apple, potential extra Hex damage, and the option to hit another enemy and freely disengage as a Swashbuckler, so something worth having in your repertoire even if only used occasionally.
If I were her I would (eventually) take 5 in Warlock to take advantage of various pact weapon upgrade invocations, including an extra attack and or Eldritch Smite.
With a free disengaging melee Rogue it is easily the best cantrip in the game, as it both stacks with sneak attack and gives them extra thunder damage if they then try to follow you. At fourth level Warlock she learns a cantrip, so if she doesn't know Booming Blade yet that will be the time.