I think she would *like* to go away with friends, but as they are all in couples it's not possible for her.
Are you and her really sure about this? Has she been rebuffed or does she just assume that this will be the case? My parents are part of a social circle that have gone away on weekend breaks together for some years and wouldn't dream of not continuing to include the ftriend who was widowed a coupld of years ago in their plans. Even if they weren't in the ahbit of going away together she might be surprised by the response she gets if she is the one to suggest a weekend break for a small group of friends together. The secret is to not fo away as a 2+1 but ensure that the group is larger than this - it gives everbody more freedom to pick and choose what they'll do or not do together.
But it also suggests to me that perhaps the problem is not about at bottom about holidays at all but rather that your Mum is struggling to establish a social life for herself that doesn't revolve around coupledom? I suppose in the event of a divorce it is inevitable that people will tend to gravitate towards on or othe partner - especially if they knew one of them before they became a couple - but it ahs saddened me to see how sometimes those who have been widowed find that the invitations to join old friends for a night out dwindle. It must be a double bereavement - osing not only your partner but also people you have thought were good friends. It happened to a friend of mine who was greatly distressed by the whole episode when she had enough on her plate being left a widowed mother of a young teenager.
So perhaps, rather than focussing on what to do about holidays in future you do what you can to be positive and encouraging about helping her to find develop a more varied, less 'coupley' social circle? Once she does this, the holiday problem might solve itself as one her new friends could become just the holiday companion she's looking for. Perhaps even suggest that you do things with her that would help her do this so that she's not on her own when she first goes - it's something of a cliche but night classes can be a really good way of meeting new people that you do have things in common with. Salsa dancing has been my route into a a social circle that includes both singles and couples (including those who met at classes!) and a wide range of ages but it really could ahve been anything.
SM