The other thing to consider is how much of the toy is actually silicone. I know a lot of companies put very minute amounts of silicone in their toys and call it silicone, when it really is still mostly rubber/vinyl/latex. If the packaging doesn't say 100% silicone, it's probably a blend.

Try a condom over it and see if that helps. Years back women had silicone implants for the breast, some leaked causing a variety of reactions. A foreign body is just that, perhaps it is the material. Generally we hear of those who have latex allergies; however, I would never say "no, not an allergic reaction". If she is too rough with it, that can cause soreness. But when you introduce a new "material" and there is discomfort, rule is remove it and see what happens. Often you see people with tissue damage from "itching" and if you trace back you find they changed laundry detergent and have a reaction to the new product. Obvious is remove the substance.

I have never encounttered a silicon allergy. Latex, yes; silicon, no. Use a polyurethan condom as Sera describes.