While I agree that Jane Grey may not be regarded as having reigned, I have always held that Matilda should be thought of as the first Queen of England. The usual argument is “she was not crowned” but nor were Edward V and Edward VIII and you would not leave their names out of the list of monarchs.
When her father died, Matilda was de jure sovereign. Stephen succeeded by “right of sword”. Her reign de facto can be said to have begun on 7 April 1141 when she was in control of London and more of the country than the forces loyal to Stephen, she had been proclaimed “Lady of England” in Westminster and she had Stephen locked up a captive. Clearly she was in charge and Stephen was no longer King de facto. Preparations were made for her coronation.
By November in the same year, the tables had turned. Defections had forced Matilda to quit London and Stephen was released. To emphasise he was King again, Stephen had a second coronation. I believe that Matilda can be said to have reigned after her proclamation at least until the military defeat of the Rout of Wincheser on 14 September 1141 and probably until Stephen was no longer her prisoner (1 November).