Let me add what we did while running way over the weight limit in the lower class:
Get the seat as far left and forward as you can, you won't be adding any lead. If that #170lb kart has lead on it, take it off.
Get the seat as low and laid back as you can and mount it with some play in the mounting bolts
Move the right side wheels out, the left sides all the way in.
I found moving the right rear tire/axle back (increase right side wheel base) helped a lot.
If she struggles with power, ask the track if she can get an exception to run a one step bigger restrictor plate or bigger cam (might be a wink and nod deal with tech inspector)