Fight the remaining 8 gym leaders.
Board the SSAqua at Vermilion city. Do all the stuff inside and when you get out you will be in Kanto.
You will initially find her bugging the poor Captin of SSAqua. when she is playing hide go seek, go down 1 level see her hiding on the oter side of the ship almost completely covered by the wall in you line of vision. As you will see, she is a very good Hider.