Epona is usually depicted as a woman riding a big white horse.
That's all I got. The Celts were a preliterate people. We only know what Irish monks decided to record later on, and they had a vested interest in erasing goddesses (and little g gods) from history.
But I think you can work with that, Pasadena Adjacent, because you are an artist and and a very creative person. Also, you are a person with a social justice streak, and I think you can reclaim Epona and invent a whole backstory for her.
In honor of all things Irish, I say start with a limerick. I'll start it for you.
There once was a goddess Epona.
Who rode on a pony named Jonah.
She turned into a mare, and said "What have you there?"
Channel this goddess: When you want a horse, when horseback riding, when listening to "Rhiannon" by Stevie Nicks. Rumor has it Epona was transmogrified into the tragic Welsh heroine Rhiannon. Finally that song makes sense!
Need a goddess? I got goddesses, and normally I know much more about them. (Blast those Monks! Although, apparently, they also saved western civilization, so I guess we have to cut them some slack.) Anyway, to get your goddess, post a comment saying what you want one for. Then check back in a week or two and see what you got. It's fun! It's free! It's a way better gift than a toaster.