Resisting Bedtime

DD1 has lately (the last few months) been pushing boundaries in relation to bedtime. Initially, it was coming out for an hour or so after bed time, but easily coaxed back to bed. The time she mucks around for has gradually gotten longer, her stubbornness about going to bed increased, the tantrums gotten louder and longer (most of which wake DD2). Lately, I'm lucky if she asleep before 10pm.

Everything I say to her is met with 3 year old back chat, every excuse she can think of is used - at 10pm tonight she was playing in her room, light on, as she was 'scared of the dark'. She may well be but that only came out when DH asked her if she was - I wonder if the idea was put in her head, rather than her actually being scared of the dark (especially as she has a rather bright night light and this was the first Id heard her say that).
She has gone to sleep finally tonight after I let her hop in to bed with DH. Trouble is, she is awful to sleep with - loud sleep talking, lots of thrashing about, so co-sleeping isnt something I want to do if DH or I are going to get any decent sleep. We have cuddled her to sleep with little success - she wakes as soon as we move.

We've tried later bedtimes, earlier bedtimes (in case she was overtired) - neither worked. I try to take a gentle approach and don't want to just shut her door, but I'm out of ideas, and almost out of patience. Help?!