Seems like the firing is too fast.
Did your work blow up in a bisque firing or were you trying to raw fire your work in the glaze firing of her bisque ware? If the latter, that firing schedule is too fast - your pots need to go through a slow bisque firing. If you continue to fire with her, she will need to adjust her firing schedule to accommodate your clay's requirements. If she is unwilling to change her schedule, maybe its possible for you to rent the kiln from her and do a full load with only your work.
- MMead likes this