Try learning English, he didn't say Flemeth is Isabela or Isabela is Flemeth. He said that BOTH characters that were in Dragon Age Origins are going to be in Dragon Age 2. Isabela /is/ in DA:O, she's in the Pearl, the brothel that you can visit in Denerim. She still has her ship then and you /can/ have sex with her, or if in a relationship with anyone but Morrigan, you can have a threesome even.
My point stands, in DA:O they explain she'd look for a magic using female body, Isabela has /no/ magic whatsoever, as she's a rogue duelist as she was in DA:O, because she can train you to be a duelist or train your rogue party members.
Actually, you can have a foursome along with Zevran, and with Leliana if she is hardened and you chose the correct answer after the hardening part to make her more loose. I am unsure about Alistair, but I would imagine so since Zev goes both ways.
[Edited by tommy6860, 3/7/2011 6:15:19 PM]
and btw Flemeth is Isabella :P watch the whole video:
Link
I think you need to watch that video again, because nowhere in that video does Silverman say that Flemeth is Isabela or the opposite. he only says that Isabela is in Origins as well, nothing more. Go to about 2:35 into the video and listen, it is pretty clear and how you got what you claim from Silveman's words is a mystery.