de-degreaser?

My girlfriend had a fire in her apartment and used a cleaning service (Servpro) to clean and remove the soot from her belongings. However, they used a chemical degreaser (she's not sure what, but it has a citrusy smell) that, even more than a year later, has left a tacky residue and odor on all of her stuff, especially her many boxes of art books. She's very chemical-sensitive, too, so this is a real pain in the ass. Any thoughts on how to get the residue of this degreaser off her books?