For what it's worth I typically go by this rule in the field and it hasn't let me wrong YET.
If it's a routine ALS, I get my BGL via IV hub.
If my clinical treatments will be based off my findings (diabetic emergencies or possible CVA) I go by fingerstick.
My other question for you is... Was she bradycardic prior to the D50? If so maybe you could have done a fluid bolus with D10 vs a D50 IVP? But I was not there, your the quarterback =)