Angela, Your daughter sounds very special.......as does her concerned mom! Not sure what the "glaze" is that you mentioned she uses to join pieces of PC. People usually use TLC (Transulcent Liquid Clay...it's made by Sculpey) and would be in the PC (Poly Clay) area of your craft store. A small dab of it applied with a toothpick, or a small paint brush, will temporarily "tack" uncured PC to uncured PC, as well as cured to cured and uncured to cured. It's the universal PC "glue". Note: if too much is applied it will show as a shiny bit at the seam.
Just in case she is using Sculpey III PC.......... As far as keeping ease in breakage, the majority of folks who work with PC do not use SculpeyIII because it's mushy to work with, brittle and notoriously VERY fragile after curing. I've been a PREMO brand fan for many years. I regularly drop cured jewelry components made from REALLY well cured PREMO (longer than the label specifies) and they have never broken when they hit the laminate flooring. In the USA, at least, PREMO brand clay is easy to find in craft stores. Some prefer Kato. In Europe many use Fimo.
It's also possible that there is something that needs to be tweaked in the curing (cooking process). If not cured long enough at proper temperature the clay will appear cured, but will break easily. A properly cured 1/8" thick piece of PC (2.87mm) should allow for some flex in it when bent a little, but it shouldn't break...(unless it's SculpeyIII) . Use of an extra thermometer can be very helpful as the thermometer on toaster and other types of ovens can be extremely unreliable. Lining the bottom of a toaster oven with clay tiles can be helpful as it evens out the tendency for the oven to spike in temp. If you are located above 3,500 feet (1066 meters) you have to cure longer and hotter than the label specifies (I can give you recommendations if you need them).
Curing clay articles: Ginger from Blue Bottle Tree tutes, 3 parts
curing temperatures http://thebluebottletree.com/baking-polymer-clay-temperature/
My PC hints for beginning clayers, especially use of thermometer:
p.2 is a list of URLs to PC resources including tutorials
If you or your daughter need further info on the current question or have other questions please don't hesitate to ask by posting in the "Questions Folder". PC knowledge is something all of us here try to pass forward.
Anita in AZ