Breaking habits 18 month old

[Twistedheartache]

Hi,
Hope somebody has some tips. Dd2 wakes after 4 hours & screams the place down until I take her to bed with me.
I'm not fundamentally bothered about co-sleeping it's just inconvenient if I'm still doing jobs/pottering downstairs & am not ready for bed & she's a touchy feel child so constantly mauling me in my sleep.
Any ideas why she would wake up? She's like clockwork
Any ideas on how to keep her in her cot? After 35 mins of getting her back to sleep in her cot last night she stayed for less than 10 mins once I'd gone.
She's slept through X2 in the last couple of months (slept like an angel til 5.5 months when she stopped) & she's miles better than DD1 was so it's not a massive deal I just think it's fixable.
In case it's relevant she has moderate hearing loss so is obviously unaided in the night so I think that must be a bit scary for her when it's dark