How do i tell my mom?(Wiccan)?

I was born and raised a catholic got baptized,holy communion, the whole nine yards.I lived with my grandparents and my grandparents are the "If you don't go to mass on Sunday your going to hell" kind of people..Very religious..As i was growing up I was forced to put on a nice little dress and go to church every Sunday which i hated to do..and as i got older i would just not go..and i would get the whole scolding and the devil is watching you lecture but they would always just leave it and go to church anyways and i would get the silent treatment..but the next day everything would turn back to normal.. Then i moved with my dad in Colorado..(i lived in Texas before) and he is not religious at all.he is also a paramedic works 24 hr shifts..so while he works i stay with his best friend..After staying with her for a few months i found out she is a witch(10+ years)..and explained to me what she believes in..and the way the Wiccan religion is..And why she doesn't tell people who her or her family are because people are afraid of what they don't understand.. After i did a bit of research i asked her if she would teach me the Wiccan ways and she agreed and said she would be happy to teach me:)But the thing is my mom is coming up to Colorado for a few days to see me and i don't want to change who i am and cover up everything..my mom should except me for who i am... christian or not..So how would be the best way to bring it up with my mom that i am not catholic anymore?