Police are appealing for witnesses to the event, which took place at about 10.55am.
The female was walking in Kelvin Gate in Bullbrook from the direction of Deepfield Road towards a pedestrian walkway when she heard a loud noise and felt a sharp pain in her shoulder.
She believes she was hit by the pellet, which penetrated her clothing, and caused her to sustain bruising to her shoulder blade.
Two woman were walking ahead of her at the time of the incident, and continued walking away from her towards a roundabout.
Investigating officer PC Jon Morris said: "I am appealing for anyone with information about this incident or who saw what happened to contact police.
“Perhaps the two women walking nearby saw something which could help with the investigation and I would urge them to speak to officers.”
Anyone with information should PC Morris on 101.
Or to call anonymously call Crimestoppers on 0800 555111.
- A 15-year-old boy from Bracknell was arrested on suspicion of possessing a firearm with intent to endanger life/enable another to do so. He was released on bail until Sunday, January 12.