Dondobot Pronam to all devotees.
In Dwapara yuga, when the sakhis(Gopis) of Radharani heared the fact that their beloved Krisna had returned to Golok-Brindabon ending his lila in the Earth, then they bacame so shocked that all of them left their material bodies then and there and went back to Golok-Brindabon.
After their spirits left their body, their bodies soon converted to a special type soil called Tilaka-soil in Brindabon.All the Baisnaba use that soil on their forehead and many other places of their bodies. And as that soil is made of Tilaka which we get from the bodies of Gopis, so that is called 'GOPI-TILAKA'.
So the question of using Gopi-tilaka by any gopi or Radharani do'es not arises.
I have learnt the above explanation from His Grace Prohlad Nath Probhu at Mayapur. If you know any other explanation regarding this, then pls enrich me.