If she doesn't have any children with her it's an adult trip that's how things work. Doesn't matter if she's gone to Disney, universal or timbuktu: no kids=adult trip.
Sian hasn't done just done adult trips without her kids, she's done them with random insta huns who are her "besties" for 5 minutes. She's done at least 2 of these trips and tried to do a trip which was just her and Callum. She's not a single mum using her own money while her child is in the care of their other parent on their designated time. She's someone who bangs on about budgeting and having to really skrimp on day to day things to go away like they do (which is a complete facade anyway) who then chose to spend family money on just her going away on expensive trips away.