Three males carrying balaclavas entered the Cheshire Cheese pub in Doseley Road at about 10.15pm on Monday.
One man is reported to have pointed a weapon – believed to be a knife – on the lady and demanded money.
The victim removed a quantity of cash from the until and money was also taken from her wallet earlier than the men fled in an unknown route.
The girl suffered slight neck accidents and was left shaken up by the incident.
The primary man is described as white, around 6ft tall, of slim build with brown eyes and a Official deep voice. He was believed to be carrying a waist size shiny black Puffa-model jacket, black full-fingered gloves, a black watch on his right wrist and plain dark charcoal colored cotton jersey jogging trousers with cuffs round ankles.
The second man was reported to be white, round 5ft 6in, of medium build, with darkish facial stubble. He was thought to be dressed in a black jacket which had a large Stone Island badge on one of the higher sleeves and spoke with a local accent.