wow,thats pretty old for her size pot,generally u do want something taller rather than wider.adding fresh soil wont do anything to help a root bound plant thats staying in the some container.if i were u,i would try and find a planter twice as wide,put your plant basically into a make shit dwc system to loosen the soil,pull the plant out after the dirt is loose enough to play with then with gloves on lay your root mass down side ways.this might buy you more time,then i would take a shit load of cuttings,saving your best one for use as a new mother.like i sed this is if it is a last resort.theres no way to just move here and go buy 2 or 3 cheap as 2 ft flourescents?shit u could even use a card board box and keep her sperate from the rest if u had 2.