I think there is a lot in the above.
You do seem in two minds about this.
I also think it is a communications issue.
But while I agree her behaviour does come across as inconsiderate and perhaps selfish. Perhaps she doesn't realise or thinks she is just being assertive. She takes your acquiescence as being OK with whatever it is.
Sometimes people don't speak up because they've been brought up to go along with their elders and "betters" or because they've been made to feel it would be rude or impolite. Or they've been taught that speaking up is confrontational and have faced retaliation in the past. Others may be more forthright in organising things to suit themselves... and I think people become more confident doing that as they get older which might be why it becomes more apparent.
I think you need to redefine the terms of your friendship. At present, she decides something and you feel the choice is go along with it for the sake of the friendship or risk an unpleasant confrontation blowing the whole thing up for good. But before you do that, you could see if it works to get your point across to her a bit better, and question why she does things without communicating properly with you.
So I think it would still be a good exercise to talk to her about this in a non accusatory way.. along the lines of "Friend you may not even realise but I was quite hurt when you booked the place on your own with no further discussion. I've been trying to imagine what I will do whilst we are in different hotels. I don't see the point in going on a trip together and then not actually being together. Its not how I envisaged things when I agreed to come. How do you see it working? and see what she says.
Personally I agree with you a trip where you have to stay in different hotels is a bit pointless, and would make me feel a bit lonely but equally I don't think she owes you to pay for you. It could be that she thought I did it OPs way last time and didn't like it and maybe she resented it, just like you are resenting her decision now and thought I'll do it my way and maybe OP will go with my hotel.
And then you will have told her how you feel without having an argument or assuming what her motives are. I think she might actually be a bit mortified, "I've not saying this to upset you or fight with you, but I think we are old enough to be able to withstand a bit of honesty from each other." Give her a chance to think about it and see if she offers a compromise or even understands what you are saying.
You can then choose whether to to carry on, dial it down, or leave the friendship. But it will be your choice, on your terms. It may backfire of course, but at least you've given it a go, and given both of you a chance and even if it does backfire, you will have said your piece in a way that she will have been able to listen to without shutting it down immediately.
Anyway, only you know the situation in RL but good luck with whatever you choose to do.