Introduce porn, anything she feels comfortable at first. Ask her what she things about you giving her pleasure while you watch porn together. One thing that worked wonders to me was to let her watching it while I pleasured her without looking at the screen. She felt freer to look and choose. You can also add new toys to increase the chance of a BBC toy. You know her, so details are with you.
Is it possible she already has somebody in mind and that's what made it click with her? In any case, this phase may last a while and you better let it take its time. Don't ruin everything being too hasty and needy. In her mind it must be a lot about her. Your fetish must just a helpful detail for HER desires.
See how far you can get with this. One way it may go is how it went to me. Our sex life went so far into the fetishes and roleplays that I was already servicing her and acting like a cuck in bed, licking her while she enjoyed a BBC dildo, and licking her afteward (sometime licking the dildo a bit), kissing her after she sucked the dildo a lot, and helping her with all of that in a very cuck way. Adding the real thing was a mere obvious step.