When should my friend apply for a one year extension of her non-B visa?

Good evening!

My friend has got a 1 year multiple entry non-B expiring August 23rd, she has just come back from a visa run so her exit stamp is for a month after that. We have to apply for the one year extension based on employment, should that be done before the non-B visa expires or before her new exit stamp expires? (The work permit was just renewed two weeks ago).

Thank you!