After you restored order by finishing the quest My Kind of Town, she and her husband return to their home at the Mojave Express Building. Most of the time, when you visit Primm later, she can be found walking outside, smoking a cigarette.
If you have only four radscorpion poison glands in your inventory and take them to Ruby, the dialogue option will state "I have a bunch of radscorpion glands." If chosen, the four radscorpion poison glands will be removed but in return, 5 of Ruby's casseroles will be obtained.
Killing this character would not affect your karma, but If you kill her husband Johnson Nash, you'll lose karma.