I very much doubt that the average monster girl would be particularly "widely experienced" or be keen on casual sex (casual in the sense of "uncommitted/not leading to something more"), at least not in KCverse, which is the only defined 'verse most of this board uses, much as many gripe and wish otherwise
Let's break it down; the average Mamono:
>Is obsessed not just with fucking, but with getting married/mated and raising a family
>In intense competition for prospective males with other MGs
>Biologically incapable of infidelity
>Operates under the belief that "sex=love"
>Have ridiculously low standards/operate on the "I can change him" mindset (which actually works out alright thanks to the effects of incubization)
>The girls who do have high prerequisites consider "worthy of sex" to be the same as "worthy of lifebond" because, again, to KC sex=love
It's honestly just basic common sense to assume that a girl would consider the first dick she succeeds in impaling herself on to be "The One".
Obviously some amount of fall-through has to would happen: The man turns out to be morally reprehensible, he's an Orderlite and manages to run away before getting brainwashed shown the light, he Alps, if the girl is civilized, they might even have incompatible views on key aspects of relationships (e.g. Acceptiblity of harems), but these would be exceptions.
Virginity wouldn't be valued in monster society the same as humans would (a matriarchal civilization doesn't have the same cause for anxiety in regards to succession/bloodlines as a patriarchal one for obvious reasons, and infidelity/promiscuity flat out can't be done by Mamono anyway) but a girl who's been around the block plenty and is still single would definitely get side-eyed for at least the "why can't she keep hold of a man" angle.