L.,
Nightmares are a possbility, but you'd probably know if that was the case. She'd probably have cried out at one point in the night after she was sleeping for a while, and you'd know if she had been afraid. Fear in a little kid is easy to pick up, and it doesn't look like regular opposition. If you can think back to an instance like this, then nightmares might be it.
She may be dealing with typical toddler fears of the dark, but you'd probably know that one, too. It's common around this age, but again, fear looks different, and you'd know it in your child.
My best guess is that she's figured out that life doesn't stop when she gets sent to bed. Mommy and Daddy are still around and awake. Her toys are all still there, etc. Why go to sleep when there's other stuff to do that's way more fun? And she's not a baby anymore. She's capable of MAKING herself stay awake, just like we can if we want to. This is probably it. My son went through this phase, too. You may be noticing it now while your husband is off because she now hears you two talking. When you were alone, you probably didn't do a whole lot of talking to yourself, so she didn't hear conversation and laughter.
Just stick with your routine and your rules. If what I explained above is the problem, it's not going to go away. You're still not going to shut down the whole house and go to bed because she does. She needs to learn that bedtime is bedtime, and she has to go when it's time. This is not easy. She's going to resist a lot, and as important as this is to you, it's a whole lot more important to her, so she's going to fight harder than you. Just keep putting her back in bed, reassuring her that you'll see her in the morning and you love her. Some kids respond well to a little chat as part of their routine about what they are going to do the next day. It gives them something to look forward to, and it's comforting to them to know that there will be lots of fun to be had when they wake up.
Good luck, L.. Bedtime battles are tough, and they typically don't resolve easily.
Jess