I think you are right to be annoyed by the lack of communication, plans changing, and extra people being sprung upon you.
Next time your friend is planning to come, be proactive and confirm the plans with her several times. You can even say, as Kaypeep suggested, "I just wanted to make sure it's only you, because the last couple times you arrived with someone else."
At almost nine months pregnant, I don't think I would have scrambled to move furniture or tidy beyond the basics when she unexpectedly changed the date she would be staying with you. As long as the bathroom and the bed sheets were clean, I would have let her navigate around the extra furniture, or told her pleasantly that she could sleep on the couch since we hadn't scheduled the furniture movers until later. If she's going to be so flexible with her plans, she should be equal flexible with her accommodations.
I also wondered why, for example, your DH couldn't take the extra family member for a walk or a drive around town, leaving you and your friend home alone to chat. Or even taken the family member into another room and watched a movie with them. If it was only you, friend, and friend's family member I can see how you wouldn't want to exile the third person off by themselves somewhere.
It also might be better to try meeting her halfway next time--each of you drive an hour to a restaurant or park, DH and family member (possibly with your baby) go off to do something else, and the two of you can chat for a while. That way you don't have to worry so much about making accommodations for her.
I know these things can be tough, especially with a friend you don't get to see too much--you don't want to give them a cold reception with a lot of rules. But it sounds like it's really irritating to you, and that there are things Friend could be doing that are more considerate of you. But, she may not even think of them until you say something.