In the 48 hours after her boyfriend allegedly stabbed a teenager in a Woolworths car park last week, Cassandra Ross was trawling the web, a court has heard.

The 23-year-old was the only other person with Jeremy Allen, 29, when he allegedly attacked the 16-year-old boy in the car park in Balmain, in Sydney's inner west, on Thursday evening, injuring the teen's abdomen and hand.

Cassandra Ross has been charged with concealing a crime after the alleged stabbing of a teenage boy in Balmain. Credit:Facebook

As the boy fell down bleeding, Ms Ross and Mr Allen fled, sparking an extensive police search for the pair, assisted by the dog unit.

They were later arrested at an address in Foy Street, Balmain.