It happened on the long cycle track running between Chamberlain Road and Tween Dykes Road around 10.30am on 20 July 18.
A man who was also riding a bicycle approached the victim, threatened her then stole a black rucksack containing a mobile phone, money, keys, a raincoat and a yellow t-shirt.
She was shaken but unhurt. The suspect has been described as white but tanned, in his mid 20s, of muscular build with short, brown hair. He was wearing sunglasses, a grey t-shirt, shorts and trainers.
Did you see this suspect or have any information? Call 101 quoting reference 16/76611/18.