I didn't know that she was catholic.
Wasn't Diana referred to as the Princess of Wales when she was married to Charles?
She went to a catholic school , but may not be , I'm sorry. (Immaculate Heart High School, all-girls private, Los Angeles)
Markle will be baptised and confirmed in the Church of England, before marriage to Harry.
WHEN Diana divorced, she lost her 'H.R.H. Princess of Wales" honorary title ( or style) she received at marriage.
She was not born any kind of 'princess' in anyway, and when she passed away, she had no HRH princess title.
ie; at divorce she kept 'Diana, Princess of Wales', and lost the 'style' of
Her
Royal
Highness.
IF Charles ascends to the throne, he as king can make Camilla 'Princess Consort" or 'Queen consort'.
but 'Queen' is out, (because of past divorce)....Meghan Markle is also a divorcee....so 'Queen' is out... 
