Sit down at a table and talk to her about it... Not on a sofa or comfy chairs. By talking over a formal table setting it takes emotions out of an argument. Especially uf you can agree beforehand that nobody gets up from the table until the conversation has stopped.
Me personally, have never mentioned my levels being higher or lower as any causation to my thinking ability. Thats me though. My hubby knows when my levels are lowering or raising which helps. He doesn't say "test your blood" anymore which he used to years ago.. Because it would upset me as 99% of time they were perfect and HE blamed my diabetes instead of listening to me-lol
).
It maybe that your partner is swinging from highs to lows with her levels and this can affect the brains abilitys.
The other thing is, to consider.... In a relationship quite often one person is the "food provider". Sometimes non diabetics do not really fully understand just what a healthy meal and snacks are for a diabetic.... And this can impact on the partner if the main food provider is a non diabetic...
Not saying that this is the case with your relationship.... But it was with mine 20years ago when I met my hubby. He the non diabetic and didn't really understand the way I ate..
I see it in other relationships, where friends have got together as couples.. He loves cooking and eating and suddenly she has gone from a 10 to a size 18... Because she has turned her food portions and eating to her now hubbys..... This isn't a one off I've seen like this.
My hubby left me to my own eating plans and continued his. I stayed size 10ish, his weight continued to balloon. 20years on, he now eats the same portions as me and has llost 4stone. So I guess in the end I have become the main food provider...
So, trying to control diabetes and have a new love in her life can be difficult.
It really is hard for a new partner initially. Hard to say without knowing your partner and whats happening with her blood levels etc... Stress can raise levels too, but at end of day whats causing the arguments in the first place? I think thats the first thing to realise...