Получих няколко мнения и общо взето нещата се изясняват:

Цитирам бувално:

А) Мнение на сингапурка (40-годишна преподавателка по математика, пребиваваща в Щатите):

I am not so good with novels and all.. but in my layman interpretation,

(1) I would take it that she cannot play devil for just a while... that she truly IS devil itself... for the things she's done. "on loan" to me is a borrowed status... as though she is NOT a devil (despite the things she's committed). But that she could not go on that borrowed status.

Also, what I was thinking was:

(2) She could not borrow any EXCUSE for being evil? Like borrowing the devil to do the bad things she did.....

I have bounced this off to a friend in theatrical studies, she's a movie director.

(3) Her interpretation is - of her not wanting to go down the path of the devil any longer.....

Б) Мнение на високоинтелигентен английски физик, преподавател в Канада:

(понеже е препредадено от българин, не го цитирам, а преразказвам):

"Смисълът е, че ако веднъж се държиш лошо или направиш нещо лошо (wicked), то винаги ще те преследва, ще стои с теб. С други думи, не можеш да бъдеш лош временно или за малко, и след това да бъдеш добър."

В) Мнение на високобразован англичанин, живеещ в Англия, техническо лице, завършил много престижен университет:

I think it might be saying that the woman in question is in a state of sin, and there's not a way she could "temporarily" be doing something sinful (she is either a sinner or not, she can't be a sinner only some of the time). The syntax is a bit old fashioned! I think you could re-write it as "she could not be a sinner temporarily" (I think "take the devil" means give in to the devil, ie to sin)

Г) Друг англичанин с неизвестен background:

I think it means that once you've committed a mortal sin there is no escape from damnation. You cannot take the devil out on loan (in the sense of a library book or film) you must buy Him completely. She's committed the sin of lust, and so the devil is now with her forever and cannot be returned.

Д) Следващо мнение на англичанин, президент на някаква фирма с технически предмет на дейност:

[...] the first two sentences say she is not going to be forgiven for her sins. So the next is repeating this: She could not take the Devil on loan – in simple language meaning she can’t expect to commit a load of sins then be good again and get away with it. In other words – once she has made a pact with the Devil, it is final, no going back

E) И едно последно мнение пак на англичанин, което резюмира май най-добре:

Could be some artistic license there rather than a proper saying. It seems to imply that there's no turning back beyond a certain point. A similar saying would be the American "no such thing as a half-way crook".

Мисля, че вече е ясно.

"You'd be surprised how much it costs to look this cheap."
DOLLY PARTON