Hi there, I have a 4 month old who has started sleeping on her tummy. No matter what I do she rolls straight back onto her tummy, I’m losing sleep over this. She is unable to roll back onto her back yet. There is a lot of conflicting information about whether it is safe to leave her sleeping on her tummy. I’m trying to teach her how to roll back onto her back everyday. She concerns me as when she is on her tummy I can only see one nostril visible and it is quite close to the mattress. I stay awake all night rolling her back continuously every hour.

Most babies will be rolling over by 4- 5 months…...some earlier, some later.           
This is normal as babies grow & become stronger.
Many babies then prefer to sleep on their tummy or side.
This is not something that needs to be stopped. It is important to make her environment as safe as possible.

Is your baby in her cot now & no longer being wrapped?
If not, she needs to be moved to her cot & be unwrapped.
She needs to space of the cot & her arms free to move safely.
Ensure that the cot mattress is firm & flat.
**Always continue to place baby on back to sleep.

How does she go with tummy time when awake?
Is she holding her head up, reaching for objects &/or rolling?

Red Nose has the following general information about rolling

Give baby extra tummy time to play when awake and supervised as this helps baby to develop stronger neck and upper body muscles which in turn enables them to roll back over.
Make sure that baby is on a firm and well-fitting mattress that is flat (not tilted or elevated).
Make sure that baby’s face and head remains uncovered (do not use lambswool, doonas, pillows, cot bumpers or soft toys)

** As babies grow and develop they become very active and learn to roll around the cot.
At this time, continue to put them on the back at the start of sleep time, but let them find their own position of comfort.
By this stage it is not necessary to wake during the night to turn baby over to the back position

Do not use any devices designed to keep baby in a particular sleep position.
https://rednose.org.au/article/what-do-we-do-now-that-a-baby-has-started-to-roll-over