My DD is the same. Nothing seems to work.
DS was the same. He would sleep longer in the hug-a-bub when he was little, then nothing worked.
So I just gave up and I'm pretty much ready to give up with DD too now. Unlike DS who really didn't want to sleep, she does and is so grizzly and grumpy most of the day. But just can't sleep longer than 40 minutes tops (20-30 is pretty normal too).
Honestly sometimes I think you just have to wrk around it. You can't spend all day trying to get one child to sleep, you know?