if your child has always been in diapers, she has essentially been 'trained' to go in her diaper. If you have been using disposable diapers, she is probably somewhat comfortable going pee in her diaper and she has become accustomed to poo in her diaper. If you are willing to endure a little mess, consider letting her be naked from the waist down and use a little potty that she can get on and off of by herself. Sometimes a new awareness of their bowel and bladder can speed up the process. Cloth diapers or even letting her wear long cotton pants also increase awareness of elimination. Sometimes feeling uncomfortable in this way also speeds up potty learning. A special book or toy just for potty time can also help. Lastly, I talk to my almost 2 year old about how I love her no matter what she does, but that I prefer she - insert wanted behavior. She usually chooses to do what I'd prefer. I also try to give specific praise instead of a general "good job" as the research I've read suggests general praise only produces short-term positive results. Long-term results are better achieved by more specific praise I.e. "Thanks for putting your poo in the potty. It meets our need for good hygiene."
I agree with AnnaM about the nonchalant mention about using the potty, too.
A little off-topic, my almost 2 year old is pretty much potty-learned, but we practiced elimination communication since she was 3 weeks old. She has on and off since 3 wks' age had varying success eliminating into a toilet, potty or sink rather than her diaper. A lot more work at the beginning, but she stopped pooping in her diaper waaay early on and that was sooo worth it! If you want info on that method for your second, I'm happy to share what worked for us.
Enjoy your pregnancy, your little one and healthy delivery/recovery with little number 2!
_________________________
"To see a world in a grain of sand,
And a heaven in a wild flower,
Hold infinity in the palm of your hand,
And eternity in an hour." - William Blake