Each bio-electrical impedance device comes with a manual that explains the proper conditions under which to get an accurate read on a client. Most differences that you’re describing, are due to a dehydration issue. It could be that with the summertime heat and humidity (not sure where you are located?), her normal water intake needs to be increased to account for these issues. The same could be true if she was traveling recently, or even is there was a change in the medication she’s been using to control her diabetes.
As Karin, indicated, it would be unheard of for her body fat percentage to make a jump like that without her weight also climbing. Did you also take measurements? I use measurements, as well as a bio-impedance scale to double check all my assessments and to decrease the chances of a dehydration issue. The tanita scale I use, also tests for hydration level to see the accuracy of the body fat reading and see where dehydration may be an issue.
If you don’t have measurements on her, I would take measurements and see if the body fat percentage you get with measurements is equal to what you saw with the scale and then go from there.