In the Middle Ages, a small, fine cloth or toilette (towelette) was used to cover clothing as a protection from insects and dust. The various and sundry articles necessary for a woman's or a man's personal grooming and embellishment were also wrapped inside such a small cloth and tucked away when not in use, to be laid out in the morning when it was time to dress.
Abraham BosseLes Cinq Sens, v. 1638 : La Vue
By the 17th century the "little cloth" might be of plain or decorated linen, or it could be a luxurious silk or sometimes even a small tapestry served as a wrapper for these necesary items. Now, the cloth, its contents, as well as the process were known as latoilette.
Jean-Francois de Troy Dame à sa toilette recevant un cavalier
"J'avais ce matin un Provençal, un Breton, un Bourguignon, à ma toilette,"
Little by little, in the 18th century, the piece of furniture supporting the toilette
very naturally became known as the table de toilette.
Elle passe des heures à sa toilette!
Clothing and all manner of finery being part of the process from the start,
a lady's dress once worn took on the same expression, la toilette.
The room cabinet de toilette and toilettes (ladies'/men's room)came later
but then someone put a halt to the spreading of the word before everything was called toilette!