I would say to try a gate, don't lock the door. Luckily we didn't have this issue, or at least haven't had it yet(crossing my fingers). That way, if she gets up, she is still in her room. If she falls asleep on the floor, so be it. You can always put her in bed. This worked well for my friend.
Another friend gives her kids two passes. They use the pass to get out of bed, but when the passes are gone, it is sleeptime.
What worked for us was just telling our daughter (age 3) that it was safest to stay in her bed and call to mommy and daddy when she needs us. Of course the first few weeks, she was calling us constantly and stalling bedtime. Her biggest complaint was she was scared of the dark. We have always had a nightlight, but then I added glow in the dark stars on her ceiling and Finally, we gave my daughter a flash light and let her read to herself or play with her stuffed animals. Gives her a little control, yet keeps her in bed.
I think give it a bit more time and it might work itself out. Just pick one thing and be consistant.
Best of luck.