She was assaulted by two men as she was walking her dog along the path, which leads off Station Road towards the River Ise.
Officers investigating the incident are asking anyone who walked along the path, which is opposite J&S Accessories, on the morning of Tuesday, April 11, between 10.30am and 1pm, to contact them on 101.
The men are both described as white, with dark hair, aged 30 to 40 and wore green wellingtons and shorts.
One of the men had a tattoo.
They also had a dog, described as black, medium-sized, with brown fur on its face by its jaw.
Anyone with information about the attack is asked to contact Northamptonshire Police on 101 or Crimestoppers anonymously on 0800 555111.