Fucking hell some of the responses on here, honest to god I despair.
The poor woman is grieving. Grief isn't linear and she is obviously really struggling and needs understanding not telling her that she is miserable and moping.
Everyone deals with things differently. Not everyone can 'just get on with it' and not everyone can just put a smile on when they are feeling broken inside.
Maybe she went because she thought it would be good for her but on getting there has realised how much she is missing her husband.
Her first holiday without him and she is probably thinking of all the things he is missing out on. God forbid that she feel a little down about it.
She probably feels lonely too. It is possible to be surrounded by people/family and still feel lonely and the void she is feeling from not having her husband with her could be really affecting her.
Have a bloody heart people.
Yes, in hindsight she probably shouldn't have come and may have been better at home.
The woman needs some space, some understanding and some gentleness and to be shown patience and some empathy. If she doesn't want to join in things then so be it. No reason for you to not enjoy your holiday too.
Put yourself in her shoes, or rather, hope you won't one day be in her shoes.