It's irresponsible to cancel plans with others without advance notification.
Hillary and her friends have had plans to go to Paris, but Hillary finds out a couple weeks early that she can't get the time off after all.
Hillary wants to continue working at her current job.
Hillary tells her friends as soon as she finds out that she can't go.
Hillary keeps the work information to herself until the night before they are supposed to leave.
Hillary's friends are disappointed, but are able to cancel her part of the trip and avoid the costs.
Hillary's friends can't cancel and are left on the hook for her costs, and they never include her on their activities again.