My 5 month/ nearly 6 month old confidently rolls from her back to her tummy, but not from her tummy to her back. She is getting to big for her bassinet so looking to move her into her own room and cot, but worried that she can’t roll back. She sleeps in her cot during the day and rolls to her side and tummy, and will cry or wake up when she can’t get back onto her back. I am also worried she’ll get stuck face down during the night as I won’t be able to watch like I do during the day. She can lift her head up if needed, but have seen her during the day sleep with her face turned into the mattress?

Most babies will be rolling over by 5-6 months. This is very normal as babies grow & become stronger.
Many babies then prefer to sleep on their tummy.

It is important that you move your baby from bassinet & cease wrapping her if you have not already done that.
This is not something that needs to be stopped, but it is important to make the environment as safe as possible for this to occur.

Ensure cot mattress is firm, well-fitting & flat.
Ensure there is nothing loose or soft in the cot.
Preferable to use a sleeping bag now that has appropriate size neck & arm holes.

Red Nose has the following information now that your baby is starting to roll.

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.com.au/article/what-do-we-do-now-that-a-baby-has-started-to-roll-over