There's no much way to tell how long it was between her Awakening and meeting with Isley. Certainly less than it took Clare to age. She cut a rather large swath across the land though, stopping by enough villages to kill Ophelia's family, and probably several other soon-to-be Claymores.
Long enough for both Riful and Isely to notice, as they had each mentioned her savagery, which must have been widespread and quite bad for their kind to notice. It doesn't seem like she and Isley waited too long after they joined together. They made the plans out right away, built forces, and started.
I'm more curious about how/when she lost her memory. It appeared her amnesia was in fact genuine. For now I'm guessing mental trauma.