Our baby can roll both ways and has taken to sleeping on her stomach, but at times is found sleeping face down into the mattress. We turn her head to the side to allow breathing but she just moves to back to face down. Is this safe? Is there something we can do about this? Thanks

What you are describing is normal development.
Most babies will be rolling over by 5 months…....some earlier, some later.

This is very normal as babies grow & become stronger many babies then prefer to sleep on their tummy, & often don’t change from that position.

How old is daughter? It is not uncommon for some 3 month olds to roll.

Red Nose actually recommends to have baby’s arms out of any wraps at 3 months in preparation for rolling.

Modify the wrap to meet the baby’s developmental changes, e.g. arms free once ‘startle’ reflex begins to disappear which is usually around 3 months
https://rednose.org.au/article/wrapping-babies

Are you still wrapping your daughter? If so, it is important to cease wrapping (or using a bag that keeps arms in) to ensure arms are free..

If she is still in a bassinet, it is important to move her to a cot.

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.

Always place baby on their back to sleep.
Ensure cot mattress is firm, well-fitting & flat.
Ensure there is nothing loose or soft in the cot.
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
https://rednose.org.au/article/is-it-safe-to-use-products-designed-to-keep-baby-in-a-particular-position