Toddler tantrum, advice needed please

Dr
So I'm 7 months pregnant with a toddler, with the new baby on the way I'm working extra hard at correcting some of these bad behaviors my daughter has developed and in pretty stumped on this one. I know this isn't necessarily pregnancy related but I figured a lot of you probably have kids as well and might have some advice for me. 
My toddler this morning was doing just fine until suddenly she started throwing her rocking horse around and getting mad about it. She wanted it to stand up correctly but she was deliberately preventing it from doing so and then throwing a fit about it. Ridiculous. (And yes I'm absolutly positive that's what was happening. I watched very closely before intervening.) I told her if she kept acting like that I would put her in her room, to which she did and then I promptly put her in bed. I sat in the room with her for abit and she started to play with her toys calmly so I left to use the bathroom to which she flipped out about. So back in the room she went. And there she has stayed, cried for ten mins and is now playing quitely with toys again. 
SO, my question is what can I do about this situation? Is there anything I should be doing differently? I'm 7 months pregnant and my patience is wearing thin. I don't think I can handle a full day of fussing to that degree and honestly her behavior in the last few months has been pretty horriable compared to the sweet angel I had previously. I know it's normal for her age and what not but Id like to nip these behaviors in the bud. I tried googling for solutions but I can't find anything that talks about the type of you throwing she's been doing where it's just an excuse to throw a fit and overdramatized.  
Any body have any advice?