I don't get it...

Friday night, Brooke drank her last bottle for the night around 10pm and went to bed around 10:45 and was back up at 2 (that's a short stretch for her)! Then slept from 2:30 to 7. Last night she finished her last bottle around 9:15 and was sleeping. I figured she be back up by 10:30 to eat again before going to sleep for the night, but she didn't. So around 10:30, I took her up to bed and she didn't wake up. I woke up around 5am for a potty break and had a heart attack because she hadn't woken up yet. She was fine, lol. I went pee and laid back down, figuring she'd have me up w/in a half an hour, but she slept until almost 8:00! Almost 12 hours! HOW can I get her to do that every night?? LOL. I'll settle for even 8 or 9 straight hours....EVERY night, lol. I wish I could figure out the trick because for the most part, her schedule is the same. I just cannot figure out what makes her sleep longer and why she varies so much on her sleep pattern at night. Maybe I'm expecting too much...Ryan wasn't sleeping through the night until he was 8-9 months old. It's just been SO long....I definitely feel rusty when it comes to taking care of a baby again! LOL. It's almost like being a first time mom again!