Shop staff and shoppers rushed to her aid when she was spotted on the ground in High Street with facial and arm injuries on Tuesday.
The trust blamed the delay on "extensive and sustained pressure".
West Midlands Ambulance Service said: "We were called at 12.41pm to reports of a patient who had fallen on High Street, Shrewsbury. One ambulance attended and arrived on scene at 3.26pm to find a woman, conscious and alert, with injuries not believed to be life threatening.
"She was given treatment on scene before being conveyed to hospital for further checks. The call was a category three call which requires us to respond within 120 minutes, 90 per cent of the time. Sadly, due to current demand on the service, this was not possible and the service would like to apologise for the delay the patient experienced."
Shopper Lucy Shrank said: "I am absolutely appalled that things have gone this way when an elderly woman has to wait for two hours for an ambulance to come for her.
"She was alert when we saw her at about 2.45pm. She was lying on the pavement and it looked like she had a nasty fall. She said she'd been waiting two hours for an ambulance and that her shoulder was hurting.
"Her face was badly bruised as well.
"Someone from one of the charity shops brought over a duvet and a pillow to help keep her comfortable."
The service explained that it has been under extensive and sustained pressure across its 999 and 111 services for several weeks due to a combination of factors including the returning of normality post-lockdown with many people out and about.
And it stated that hospital pressures had a knock-on effect on its ability to hand over patients quickly in A&E units and that the warm weather was exacerbating many medical conditions.
“Whilst it is challenging, we continue to do everything possible to provide the very best level of patient care possible to patients across the West Midlands.
"Our staff and volunteers, from every single corner of the service, are working tirelessly, responding to case after case to reach patients as quickly as possible,” it stated.