Your friend may be more moody & emotional than usual because of her pregnancy, and she insisted on visiting despite you telling her ahead of time that
you had a lot going on & it wasn't ideal, so that set you up for a failure IMO. (it may be hard, but sometimes it's just better to say "no")
It sounds to me as if she awoke from the nap (after the awkward Casino outing) and found you both gone....I can see where she'd have taken that badly-
she apparently thought you didn't want her company. Hindsight is 20:20, you should have woke her up & asked her if she wanted to go with you, or at the
very least, left her a note saying that you hesitated to wake her up, since the evenings were the only time she was expecting to spend with you.
The thing is, you say you're best friends, but neither of you was at your best in communicating with each other. I think she felt hurt and did the same in
return to you by leaving so abruptly. What a shame to lose a friend this way...maybe in time you'll find a way to reach out & talk to each other about how
this all went wrong. Everyone has "issues" at times, the thing is, communication is how you overcome the challenges.
For what it's worth, blowing money in a casino wouldn't be my idea of fun either. Since it was your idea to go, it's too bad it didn't go well. Live & learn..?