toddlers sleeping habit HELP

[user1490930230]

HI
I'm a mother of three.
I have an 8 year old a 6 years old and a 17 month old.
the 17 month old doesn't sleep. my other 2 I have been extremely strict with as they were close in age and slept perfectly.
if I'm honest because my older two are at school I don't want the younger one to wake them. Frances my younger one goes to sleep perfectly and always has done.
at the very most its 10 minutes and she is asleep soundly in her cot at 7.30, she has a sleep at 11.30 till1ish every day.
she wakes at 12 ever night and Is wide awake going crazy till3-5 then she will sleep till 8. she's not a great eater but will graze through the day. I really need help with this situation as its having an impact on my relationship and also being the best parent I can be to the other 2 children.
my partner is the main breadwinner but I also have my own business so life is extremely hard at the moment any advice will be greatly appreciated.
thank you
hollie

[JiltedJohnsJulie]

What is she doing while she's awake?