This situation can be explained by Sexual Market Theory. Men have a strong desire to do coitus with women; sure, slender women are preferred, but if the fat chick is only thing that is "open & available", and the man has had a dry spell, he will stick it into the fat chick. Men have less of a desire to have a relationship, and indeed consider a relationship along the same lines as mate selection, and so men are similar to women in that they want their mate to be of good genetics, and so men don't want to date fat chicks.
Therefore there is a Sexual Market Value (SMV) differential between what a man would stick it into and what a man would put a ring on; thus, a man's desire in women can be considered to be 3 zones: [A] women that he would marry (or date, etc., and of course which includes wanting to stick it in her); [C] women that he would not marry, but would want to stick it in; and [D] women that he would not even want to stick it in. Considering single mommies, zone [A] would be much smaller than with childless women, quite often having the attribute that a mathematician would deem "zero measure". And a man who has access to affordable professional sex services will typically have the [C]-[D] delimiter be close to the [A]-[C] delimiter, considering such women that are in this zone as being worthy of professional purchase at a free price - and this is similar to a woman's natural desire in men, as she would want to marry any man that she would want to have free sex with.
The fat chick's experience was simply one where she was in zone for this particular man. And of course it wasn't stated, but the fat chick probably had a relatively high [A]-[C] delimiter, and considered this man as being an [A], and since she finds men - who put her into their [C] zone - at this SMV level with some level of abundance, she has spurned men who are on such a low level of inceldom that they might have put her into the [A] zone. IOW, because she can get sexed by higher-tier men, she considers herself at this higher-tier herself because she has made the mistake of considering the her dating SMV as being equal to her sexing SMV.
