In English "she-devil" is recognisably idiomatic from literature, and would seem to be the best option. You say it is mainly metaphoric, but beyond fiction, calling anyone a devil (other than the devil from Christian theology) is surely metaphoric? An example of this prefix in fiction that springs to mind is in Marvel comics, the female counterpart to the Incredible Hulk was named "She-Hulk".
The idea that you can put '-ess' on the end of a term and make it female is not correct. In most cases (there are exceptions), this suffix is exchanged for a masculine suffix such as '-er' or '-or'. For example, 'actor' and 'actress' have long been the masculine and feminine counterparts respectively, just like 'seamster/seamstress', 'manager/manageress' etc. Others examples adhere more closely to the Latin feminine form, such as 'testator/testatrix', or 'dominator/dominatrix'. English has always had masculine, feminine and neuter terms - for example, musician titles like 'pianist' and 'flautist' are neuter. If you have ever seen the suffix '-ess' added to an already complete neuter term to feminise it, chances are that it has been done for artistic (likely comedic) effect and is not a true English word.
In recent years many female thespians (a neuter term for both actors and actresses) have preferred to be called 'actor', believing 'actress' to be some kind of lesser term. Likewise, you will find some references to 'doctress', but it never took hold in the medical profession and 'doctor' has been used as a gender-neutral term for some time.
Actually, it is the other suffix you mentioned '-ette' that is a diminishing suffix, to make something smaller, and is not a feminine suffix at all. For example, a "featurette" is a short film. I believe it is sometimes mistaken for a feminine suffix because of the historical term 'suffragette', but in actual fact British newspaper the Daily Mail coined the term in order to belittle the women advocating women's suffrage.