Tolkien moved away from the description of Beren and Lúthien wearing actual skins to disguise themselves. In the Lost Tales, Lúthien sews Beren into the wolf skin and teaches him how to walk like a wolf. This is absent from later versions - for a reason. Tolkien learned to portray magic with less time spent on logistics and physical technical details, and more focus on force of will and use of words.
So, we should learn from that and not revert to the earlier version. There is *no* reason for us to show enough of the transformation process for people to be taking 'how to' notes. The Hosts' advice was that there should be nothing on screen that answers the question of whether the elves are doing science or magic. Lúthien's story will have plenty of overt magic, and she does have a Maiar background that lends itself to magic beyond what elves can do - but that should be via singing magic songs or using her magic cloak (which she made by singing).
In other words, we can show Lúthien finding Thuringwethil's dead body...and we can show her transformed. Getting from A to B doesn't need to be clear.
We are portraying Thuringwethil as one of the original Ainur who came down to Arda, essentially. Her shapechanging ability should be natural/inherent, despite her being a servant of Melkor. Her thing is secrets and finding all of the information. So, no, not 'sexy' and her relationship with Sauron is a business one, so to speak.