Depends what the canon is now, but she learned from that telepath she was college roommates with, Dark Beast (possibly not canonical any more), was picked out by Professor X but refused him, and then rose in status in the Hellfire Club. Given that Emma was training mutants through them, presumably someone in the Club also trained her.
But it is possible she is (mostly) self trained in her abilities, but she has a few years on Rachel, fewer instances of being mind controlled and her telepathy is extremely powerful without the Phoenix Force backing it up, so I wouldn't personally put money on Rachel in a situation like this. Especially as Ray doesn't appear to be making an all-out attack, it's more a fit of pique than anything.