We're going through this with our 11 year old! Except it's not tantrums, it's just everything else. Sore foot, headache, thirsty, hungry, there's a noise in the room, can't sleep, nightmare (when she obviously hadn't been sleeping yet!) You name it, it's been thrown at us!
She also won't do her bedtime routine. Or she does it s-l-o-w-l-y.
This is what worked for us. Now, granted there's a difference between an 11-year-old and a 4-year-old but this might work!
We moved her bedtime up. With all the excuses and stuff we needed to move it up so that she'd get a decent night's sleep.
She brushes her teeth right after dinner. In order to get her to do this, we ALL brush our teeth right after dinner. You might need to do this after her snack. Do stop giving her crackers, crackers are carbs and they are probably just amping her up.
Then we all change into jammies. I call them my "comfy clothes" so it doesn't sound like we're in our PJs. I don't mind lounging around in my comfy clothes at night. She doesn't mind doing it because we are ALL doing it.
We stopped bedtime stories or any kind of bedtime anything. It just made her want to keep doing it instead of sleeping.
At the appointed time, she goes in her room. Earlier in the day we've set out clothes for the next day and made sure there's water next to her bed. She just hops into bed and we kiss goodnight. We ignore all "my foot hurts" etc. Everything is answered with "go to sleep, that will make it feel better."
Then we turn all the lights off in the house and go into our bedroom. My husband and I get our alone time and we often watch TV or read. It's nice and relaxing. We've found her more eager to be in bed when she knows that we're in our room.
We are very matter-of-fact about bedtime now. Doing extra snuggling is what we would LIKE to do when she's upset, but that seems to draw attention to the upset and make it worse. We used to think she needed more attention or more snuggles. That always made it worse! We do all our snuggling together on the couch, with lots of love to go around.
Bedtime is short, matter-of-fact, and no-nonsense.
Good luck!