You'll see her arrive at the end of this ...
Video: Mayor Boris Johnson berates London Assembly's 'invertebrate jellies' - Telegraph
And who is she? Boris's deputy, Victoria Borwick.
What you seem to have missed is that the absence of a Tory assembly member from the chamber meant that the combined opposition to Boris (Labour, Lib Dem and Green) had enough votes to be able to reject his budget in its entirety, provided they could take a vote before the balance of numbers...