Ok - the other thing I'd look at is trying a different cereal to see if the glucose will release slower - so maybe a fattier cereal like granola and/or a lower GI one like All Bran or a mix of the two)
If it was me, I'd also exoeriment with adding a slice of toast to see if that helped as for me toast would be absorbed slower than fruit. But if she's stubborn, then I don't know : D
Edited to,add - I've probably mentioned this before, but for people who only need tiny amounts of insulin, a pump is a fantastic choice. It would also allow you to lower her basal in the morning if necessary.