I am also pregnant with an active 4.5 year old that goes to school 3 days a week. I have some issues that also require me to "get horizontal" for a few hours at a time during the day, usually the afternoon when she is home.
I have gone through the gamut of activities and finally decided that the ones that make a big mess (like play dough and paint or glue-requiring crafts) are out because even though they occupy her, I'm left with cleaning up and that takes its toll - especially bending, etc. It's not a winning solution for me right now. So....
First of all, don't feel bad at all about increasing TV time if you need to. It's only a few weeks and there are many good quality shows she can watch while you get the rest you and the baby need. If you have TIVO or a DVR, you will be able to watch recorded programs as you need (my daughter loves Little Bill, Magic School Bus, Pinky Dinky Doo, Sid the Science Kid, Super Why, Berenstein Bears for example). Or with Comcast you have great selection of the PBS shows On Demand as well. I know it feels awful to use the TV, but it's such a brief time in her life..
You may want to get her started on educational software. My daughter started playing the Reader Rabbit games when she was about your daughter's age. All preschool/pre-reading and pre-math games. She'll likely play for a couple hrs at a time if you let her!!! Again, don't feel bad if you need the rest for now. There are also games on PBS.com and NickJr.com, as long as you can help her navigate a bit.
We also do board games and card games together in addition to more reading time. My daughter also really enjoys the Preschool Readiness books you can get at stores like The Learning Palace, Borders, Barnes & Noble, Target, etc. They keep her busy with easy matching games, basic mazes, letter and coloring games, etc. I can do any of these things from a mostly reclined position either on the couch or floor in our living room with her.
Lastly, if she doesn't already do "quiet time" or naptime in the afternoons, it may be a good time to try that again. Where she stays in her room and plays alone. Start with 20 minutes then add time as you can. My daugther stil naps for 1.5-2 hrs in the afternoon. Once in a while she won't sleep but just stays and play in her room for about 1 hr.