I am following all safe sleeping recommendations but my 6 month old has started rolling on to her tummy in her sleep. I have woken up a few times in a panic to find her face down (face fully pressed into the mattress). I am panicking that this will cause her to not be able to breathe. Is it okay? If not, how do I stop it from happening?

Most babies will be rolling over by 4- 5 months. This is very normal as babies grow & become stronger.
Many babies then prefer to sleep on their side or tummy.
This is not something that needs to be stopped. It is important to make her new environment as safe as possible.
https://rednose.org.au/article/what-do-we-do-now-that-a-baby-has-started-to-roll-over

Some babies also face plant at times.
Ensure that the cot mattress is firm & flat & there is nothing soft or loose in her cot, especially as she is face planting at times.

Is your baby still in a bassinet or now in a cot?
Are you still wrapping/swaddling her or does she have arms out?
Baby needs arms free & the space of a cot to roll well & safely.

You can try to gently- turn her face if you see her with face down, but often, like rolling to tummy, babies will just go back to their position of comfort.
What happens when you roll her back? Does she wake or roll straight back to tummy?
Have you seen her roll both ways?

**Increasing tummy time when awake is recommended to help build upper body strength so she can roll easily & well.

Always continue to place baby on back to sleep.

Red Nose has the following general information now that your baby 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 toysAs 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