You can be both. Honest. Phillipa is Epona and vice versa. Epona knows things now because of being Phillipa. Things she didn't know before. Things like humanity and parents and the nuts and bolts of living day to day. You'll figure it out.
Maybe you can just frame it differently? You can think of me as Javi if it helps. You can also just think about how you're talking to someone who would like to be your friend. Don't think about the god stuff if you can't handle it right now. It'll come sooner or later.
You're not being selfish. You're coping. The way I get it, a lot of us haven't told people yet. Some of us have been outed, though. Like Triton and Aphrodite. Come to think of it, a lot of the Greeks. Go figure.