I have a 16 week old baby who is obsessed with rolling onto her tummy during sleep. She rolls onto the tummy during settling time and also in her actual sleep. She is very strong and has good neck control. She began rolling tummy to back at roughly 2.5 months but since starting to roll back to tummy it's like she has forgotten how. I had read that she needs to consistently roll both ways to sleep oj her tummy. I'm so worried about her sleeping on her tummy but I am spending hours flipping her back over and having no success with her staying there. I'm just not sure what to do? I can't stay awake 24 hours per day flipping her onto her back constantly. Some naps, she will roll onto her tummy 6 or 7 times in 10 minutes.

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 she in a cot now, not a bassinet & no longer in a swaddle?
She needs the space of a cot & arms free to roll well.

Ensure her mattress is firm & flat & that there is nothing loose or soft in the cot.
How does she go with tummy time when awake?
Now that she is learning to roll, increase her tummy time when awake to help strengthen her upper body muscles.
Always continue to place baby on back for sleep.

Have a read of the Red Nose 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.

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

You are not expected to keep waking at night to roll her back, especially as she rolls straight back, & she is capable of rolling both ways.
I’m sure she will soon be seen to regularly roll both ways - some babies take a little while to want to roll back from their tummy, but she probably changes her position during the night at some stage.