Baby wont sleep

My 9 month old will not sleep unless i breast feed her to sleep. Its been this way since she was born... She started gagging today while i was breast feeding her so i tried to walk her to sleep but no she wants to breast feed, we try again and same thing. I know she is full so she isnt hungry. I think she may just want something to suck on but she refuses anything else. What are some other ways to get baby to sleep?