Hi, my 2.5 month old baby has just rolled for the first time tummy to back. She can’t roll back to tummy and has shown no signs of trying to. Can I continue to put her to sleep in an arms in sleep sack (love to dream or ergo pouch)? Or does she need to be arms out now? It seems logical that she would only be at risk if she could roll from her back to her tummy, but she can’t. So can I leave her as is with arms in until she rolls back to tummy? Her sleep sacks are not tight ie her arms aren’t pinned down beside her she moves them around within the sleep sack.

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.
This new environment involves being in a cot (not a bassinet) & in a sleeping bag with arms out.

She needs the space of a cot & arms free regardless of which way she is rolling.
Once she has attempted to roll &/or looks like being successful, then she needs to be placed for sleep in her cot with arms out of any swaddle.

**Always continue to place baby on back for sleep.

Also, nothing soft &/or padded in the cot at this stage.
Increase tummy time when awake, to continue to build upper body strength

Red Nose has the following general information now that she is 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