Cats, by nature, are most active at dawn and dusk and tend to sleep a lot - although most of the sleeping is done in 'cat naps', when they're still extremely aware of what's going on around them, and will wake at the smallest non-routine, sound. They do get some deep, REM sleep, but not as much as you would think! They can adjust a bit to your schedule - for example, I get up around 4:30-5:00 am, and now they both think it's always time to get up (even on Sundays!). The funny thing is that they seem to adjust for daylight savings time all on their own! I think you said you're often active in the early hours - she's probably thrilled to wake up and have a friend active with her.
I think the pouncing may be more in play - do you have any interactive toys (hey, even a shoe string will work), or a laser pointer (do not shine in her eyes). A lot of cats enjoy these toys, but only in short bursts - cats do not have a lot of long-duration stamina. Just don't leave toys like shoe strings out - you do not want her to try swallowing it!
The under-the-sheet deal is classic cat - they think there's a mouse or other prey down there, and will pounce on the 'prey'...they do not realize it's you. She's trying to play - and that means she's feeling more and more comfortable in your house.
I would suggest, if you have a chance, getting a book on cat behavior, and a lot of libraries can get the books for you if you want to read before you invest in buying - cats do react differently than dogs do, which can be a real change for people used to dog behavior. I love Pam Johnson-Bennett's books - she's a certified cat behaviorist,, or the Cats for Dummies book was very helpful to me when I got my Dharma and didn't know what the heck she was doing. I actually called the vet when Dharma kept falling on her side in front of me - I thought she was sick, and was gently told that falling down and showing her tummy meant she trusted me.
I was so glad to see your posts as well - I was worried that the vet visit hadn't gone well, or that your family had wanted to send Maggie back. Believe me, it's a time of adjustment for all of you, but for so many people, once some time has gone by, it'll be hard to believe Maggie wasn't always part of the family.