Unless she risks injury, don't approach this situation with the thought of "how do I stop this?" If you do in fact find that your child is on the spectrum (or even if they aren't), coping mechanisms present in many different ways and if you try to force them to stop a behavior that's helping them cope, you'll just be causing them more stress.

Thank you guys for all your comments they all have been very helpful. She has been a little ill lately, however she was doing it before we all got ill. The doctor has prescribed some drops to help clear out any wax but i will also keep an eye on weather it may be due to sound sensitivity or other factors.

My boys cover their ears or plug their ears when something is bothering them. Usually noise but my oldest recently started doing it in the bath so he wouldn’t get water in them.

Maybe make a note every time she does it and see if you can find something in common (like maybe it’s every time the vacuum is on etc?)

She is most likely doing this because of sound sensitivity & she’s overwhelmed with sounds. Sensory processing disorder is common for ASD kids. You can help by offering her noise cancelling headphones. If you are concerned I advise you to take your daughter to a developmental pediatrician.