Nemetona, Goddess of the Sacred Grove, had her cult in those dense Germanic forests that the Romans feared so much. Especially after the disaster in 9 CE, when three Roman legions and their auxillaries were ambushed and cut down in the Battle of the Teutoburg Forest, they preferred open spaces to the forests in which the druids and others worshipped.
Celtic goddesses went in for divine polyandry (multiple husbands) in a big way. For every Rosmerta or Nantosuelta who kept to one god, there were several like Damona and Ancamna who doubled or tripled up with Gaulish, Roman, or “blended” gods like Apollo Grannus or Mars Smertios. (While it is true that the Roman gods Mercury, Mars and Apollo take on different names and partners, they are the ones who take on Celtic by-names, while the goddesses keep their own.)