Not surprising really, usually practice nurses aren't specialists in diabetes, next day they'll be running the asthma clinic, weight loss clinic, baby clinic, doing smear tests etc etc. Diabetes is a complex condition and they may only know the basics. Some tend to dismiss as 'impossible' anything you report that doesn't match what they expect - but we're all different and bodies react differently.
Your nurse sounds willing to admit she doesn't know the answers and to learn, which is good. But if you're having difficulty and she seems flummoxed, ask to be referred to a specialist. Or suggest she discusses your issues with a specialist (doctor or specialist diabetes nurse) and get back to you - helping you both learn.