Previously they couldn't technically disfellowship you for marrying a non-J.W., however they recently "clarified" their translation of one the words used in a Bible verse they use to justify the disfellowshipping arrangement. It used to be translated "loose conduct" and was generally applied to behavior of an adult nature. That is now translated as "brazen conduct", and can include brazenly ignoring the repeated scriptural counsel from elders on a matter
So if the elders are aware of your relationship, they may choose to repeatedly counsel her on the issue, warning her of the dangers of marrying a non-JW. If, in their minds, she "brazenly" ignores their Bible-based counsel on the subject, they hypothetically could choose to charge her with "brazen conduct" and disfellowship her. It's really up to the discretion of her local elders.
If she chooses to keep your relationship or marriage plans private, the elders wouldn't have the opportunity to counsel her repeatedly, and therefore she wouldn't get the opportunity to display "brazen" conduct.