I have never known such a performance from a grown woman. DM is diabetic. Her blood sugar is out of control. She helps herself to biscuits & chocolate bars etc. Every morning she claims her blood sugar is so low she needs 2 spoons of sugar in her tea, this is despite her blood glucose readings of 12, 14, 18 and even 21 this week (normal is between 6 & 7). Low is below 4.
Yesterday she had an opticians appointment. I got a frantic call from nephew (DM lives with sister) because DM was having a temper tantrum because she was refused sugar in her tea (glucose 12.5 before breakfast). She was refusing to get dressed and wailing like a banshee. She was vile to my BiL and caused my sister to be late for work - keeping a sitting judge waiting. My nephew recorded part of her tantrum because I thought I wouldn't believe him. It was truly awful, when I say wailing I'm not exaggerating.
When I challenged her she said they're all liars, she never has biscuits or chocolate. She's never asked for sugar in her tea etc.
I feel (and my sister) that I am at my wits end with her. If she was a toddler we could make her sit on the naughty step, or whatever parents do with toddlers. A grown, adult woman who has agency & capacity but choses to behave like a spoilt child? What can I do?