I bought Nightfall and considering getting factions

Can I use my nightfall character to complete factions? If so how would I get her there. Really need the points for finishing it and the sweets but not wanting to make a new character

thanks

Yes
Talk to Funwa Shento in Kamadan, Jewel of Istan

source:
http://wiki.guildwars.com/wiki/Cantha#Getting_to_Cantha

awesome ty so much

Yeah, if your at the required level (10) and got to consolate docks atleast, and got bought the expansion, the npc there will offer you a quest that brings you there.