Totally unreasonable to cancel friend at such short notice; it's very hurtful, and just bad manners. She presumably has booked annual leave, maybe bought some clothes, maybe has an animal and has booked a petsitter or boarding kennels, etc. etc. I can understand her being thrown by your suggestion that you stay over with her, as her house or apartment may not be in great shape if she's just about to go away and has been busy. As a single person, I also think that people who are coupled up don't always appreciate how challenging it can be to be on one's own, and, since she has recently emerged from a relationship, she may be feeling low and lonely. I also find the comments about "protecting your family" somewhat absurd; it's not as if you are living in Gaza or Ukraine! But I know that kind of attitude goes with the Mumsnet territory.
All that being said, I would talk with your friend immediately, either face-to-face if you can or on the phone, but not via text or voice notes. I'd say that I was concerned about her negativity as it might blight your holiday, and would ask her if she has has second thoughts or if something else is bothering her. It sounds as if you invited her on a (kind) impulse, and she impulsively accepted your invitation, and may have buyer's remorse, too. But if she wants to come, I don't see how you can uninvite her.
In her position, I would not have accepted. When close married/partnered friends had young and teenage children, I would sometimes join them on holiday for two or three nights, but always with my own transport or good public transport available; the kind of holiday when there is a weekly flight is not ideal. I have also always had coupled friends and their kids (if any) to stay, particularly when I lived in America, and enjoyed those visits very much, but everyone seemed to be in agreement that they should not be too long, or if they wanted to come for a lengthy stay, that they would do their own thing when I was at work. The success of those kinds of holidays depends on having good conversations in advance and everyone being clear about what the expectations are on all sides. Good luck, OP!