She had, in the practical if not precise legal sense, a contract with Booking.com that she would pay them $150, and they would ensure she had a room at a specific hotel for that night.
Regardless of whether she'd booked the Ritz Carlton or a crummy Quality Inn, she had paid Booking.com for a night in a hotel. They were responsible to deliver that to her.
Halfway decent customer service would have, at the very least, entailed a room at the closest available equivalent or better hotel (not difficult in this case since it sounds like just about any property would qualify) and the cost of transportation there and back.
On another note to travelers: don't book hotels through an OTA (Online Travel Agency like Booking.com, Expedia, TripAdvisor and the like) unless you have to. Nearly every property in America now has a "best price guarantee" that lets you get the best possible price direct from them. And you'll often additionally be eligible to earn status and points on the hotel's own program.
DO book direct with the hotel/chain, or a traditional travel agent for higher-end properties who might have access to increased perks (aka Signature Travel, FHR etc.), and DO pay with a credit card that offers trip insurance so that if you find yourself in a situation like the above, you have some coverage.