Just be candid and talk to her about your desires and fantasy. My experience is honesty is the best route to mutual agreement. My wife is very shy also. She is also not to the point yet of making it real. She did however agree to get verified as a couple.
She knows I have this continuing fantasy of watching her take a real BBC and she actively enjoys partaking in role play with our Huge BBC Dildo's and sharing a portion of our adventures here on BlacktoWhite via our pics and vids. I do very happily say I think that thanks to all the sexy comments and the "Likes" and "Loves" our pics and vids have received on here are leading her in the right direction to maybe someday take her beyond only having her dildo playmates