It sounds like this is a relatively new relationship, in which case I wouldn't rush to incorporate diapers into it. You said you wished she would open up a little - if it's only early days, this will take time. Relationships take a lot of getting used to as it is, even before you introduce something like wetting diapers. If you keep mentioning it, it will start to grate on here.
Just spend time getting to know each other, keep the diaper discussion at a level she finds comfortable, and just be prepared to be patient.