@Daniel8190 The host likely has the room booked through another platform but didn’t link the calendar with Airbnb, so on Airbnb the room showed as available. It is the host who should deal with this, but all things considered, I wouldn’t trust them to do that. Take matters into your own hands and call Airbnb to reverse the booking. Tell them the host has said they can’t host you. They have the ability to see your message thread with the host.
PS re “is it possible for a booking to "skip the line" and automatically get accepted like she explained?” It sounds like this host may be inexperienced and has Instant Book enabled. An ‘Instant Booking’ is automatically accepted. A ‘Request to Book’ requires the guest to send a request and the host gets to consider whether they accept or not. Since she says she didn’t get the “usual notification of us requesting to stay”, your booking must have been instant booked.