Cristobalite forms in a body with insufficient fluxes present to act on all the silica at temps above 1200 C (2012F). Not likely the culprit in a body that has so much in the way of fluxes...and firing to only 04. But it is impossibe to know for sure what the chemical balance of the body is without an analysis of the particular cullet she is using.
Generally speaking "cullet" is typically a variable composition material....... unless your supplier has a specific analysis for the batches you are getting. So from batch to batch.... that composition might be varying a lot. Frits on the other hand are generally stable compositions. Personally... unless I bought HUGE stable batches in advance... I wouldn't use it for a clay body. Asking for variation issues in production.
As to Insight........ when you BUY the Level II version of Insight (well worth the access to the secure portion of the Digitalfire site) it has the ability to add in materials data for the MDT from around the world... just one of the reasons that I like it... I'm frequently converting from American to Japanese and Japanese to American recipes.
If the glazes are pinging.. the COE of the glaze and the COE of the body don't match. Remember you can't use the COE figures from ANY glaze calculation program for the BODY COE number. It can't be calculated by any method known yet... it must be physically measured (dilatometer ... or the "known expansion glaze" method of approximation). Calculation programs are of limited use in body development..... it is still unfortunately a much more empirical "testing based" approach....even for industry. (They just have nicer "toys" to use when doing it -tools-.)
There are differences between "virterous" as we think of it traditionally for a body and "melted" as in potentially overrfired. Generally you want an apparent poroisty approching zero in a vitreous type body....... but after you go past that mimum on the plot curve of porosity...... you will start having such issues as you are experiencing.
There is a quality of glasses (and vitrified bodies) that is called "brittleness". That can be a significant factor here when combined wit hthe seriously crazing glaze.
To see this level of issue you likely have TWO issues synergistically combining. A poor strength body and a non-fitting glaze. I'd fix the body issue first and then work on the glaze issue. Do one at a time (basic scientific method). In fixing the body you MIGHT end up inadvertantly fixing the glaze.
Professor of Ceramics; New Hampshire Insitute of Art
Guest Professor, Wuxi Institute of Arts and Science, Yixing, China
Former President and Past President; Potters Council