Officers are now "exploring" if her injury is linked to reports of shots being fired in the Old Walsall Road area of Hamstead at around 9.30pm on Friday.
The incident reportedly took place near the The Beaufort pub, Hamstead.
In a statement West Midlands Police said: "We were called to reports of gun shots being fired in Old Walsall Road - at around 9.30pm yesterday (26 August).
"Officers attended although no-one was found with any injuries.
"A short time later a woman in her 20s presented at hospital with what’s understood to be a gunshot wound to her arm. Her injuries are not serious and we're exploring whether this is connected.
"Inquiries in the area are continuing."
Witnesses or anyone with information are being encouraged to contact the force via the website live chat quoting reference number 3713 of 26 August.