Does putting an axolotl in the fridge make them spit out the gravel they have eaten?

I have an axolotl, when I first bought the tank it had some small white gravel that came with it so i put that in, then I saw an axolotl in my fish shop and wanted one. The guy told me that they sometimes try eat the small gravel so i bought a bag of bigger gravel and spread it out over the top to help stop it from getting to the smaller gravel. Unfortunately once i got the axolotl it got down to the small gravel and yesterday I saw some small white lumps in her belly, my fish shop told me if this happens to put her in a tub in the fridge and leave it over night and she should be sick and spit it out. Is this true or will I just be causing my axolotl more harm than good?