My daughter won’t sleep please help.

[sophz28]

Hi my 18 month old daughter hardly sleep or eats. I don’t know what to do. I have 2 other children aged 9 and 6. My 6 year old is currently being assessed for autism but I’m finding my 18month old much harder work. Today she’s eaten a few bites of toast and some crisps, she’s been awake for 14 hours on only 8 hours of sleep and is still not giving to go to sleep.
Does anyone have any advice please?