I think acetone will work, but denatured alcohol, or low-water content isopropyl alcohol (90% or 99% isopropyl).
You only want to do this if the epoxy is going to be in a thin layer, like paint. If she wants to encase something in epoxy, she wants to get the stuff that's made for that. If the layer of epoxy is not thin enough, then solvent is left in the mix and gets trapped, weakening the epoxy.
Note that over time, epoxy glue will yellow in sunlight. If this is going to be the outer coat, and if the colors are important, then she wants to get something that's specifically meant to be a top coat.