Medically, older women are advised against being too thin. Not only does being too thin place you in danger of developing osteoporosis., but if you need a serious hospital procedure, where you may not feel well enough to eat and drink. Having extra fat on your body can help protect you from malnutrition.
DH had bypass surgery with complications. In an 8 week hospital stay, he lost three stone - in his case, almost a good thing - but if he had been close to his approved BMI, much less so. A friend going in for major surgery was advised to put on a stone in weight before surgery.
Medical is one side of it, but my real worry would be, why you would think being a stone above your previous weight was such a terrible thing. It does rather suggest that you have disproportionate worries about how you look and how people judge you.
As for all those first ladies, are they really so 'thin'? For most of them they are really just very expensively dressed in designs aimed to make them look slim.
Some people are naturally thin My 15 year old DGS, OK not a woman, is 6ft 3inches with a 25 inch waist. Were he female he would look (in shape) like the Princess of Wales. He certainly does not diet, his build is genetically determined, his maternal grandfather was the same shape.
The Duchess of Windsor may have said you cannot be too rich or too thin, but she never looked a very happy person.
So forget about that extra stone, The only one who notices it is you. Go out and buy the designs of clothes that always looked good on you. One stone will not be sufficient to make them unflattering, then stop obsessing about your weight and go out and enjoy yourself.