Op I wouldn’t normally advise giving unsolicited advice to friends but in this instance I think you are absolutely right to refuse the holiday, right to be concerned, and I think you would also be right to encourage your friend to save the majority of her funds, and perhaps get some financial advice.
It’s surprisingly easy to blow that amount of money fairly quickly! And your friend will be very distressed. . Your friend will be making impulsive decisions to distract herself from grief , and in the not too distant future, she might look back and regret them very much.
As the relation of someone who was widowed young, who had been left a chunk of money which she blew through, and is now living very carefully on a state pension with very few savings, I would take your friend aside privately and have a serious word.
You are a true friend with buckets of integrity and I hope she will listen to you. And if she doesn’t, at least you have tried.
Be honest in a kind way and tell her that you would feel uncomfortable being beholden to her financially (and that wouldn’t make for a relaxing holiday) that she would be sensible not to make any impulsive purchases for at least a year after her dh died, and that she will definitely need that money in future. And the more she retains, the more she can make it work for her.
The elderly parent of someone I know has just been admitted to a nursing home and the fees are above £7,000 a month! So you might mention future security.
I also agree with pp that you should make a carefully worded public comment on your WhatsApp group and make everyone pause for thought.