First, there is no way, I would have encouraged, or even not discouraged Husband from changing his entire career path to better fit a party schedule.
Second, we were married when Husband was in the RAG. We picked a holiday weekend knowing that it almost guaranteed us at least an extra day and that was a smart move indeed. He ended up not being granted any additional leave; it can and does happen. He drove up the night of the rehearsal, almost missing it (thankfully we planned our wedding only about an hour and a half from base), and then returned to work Tuesday morning after the Monday holiday.
Third, I will offer you some unsolicted advice. You are going down a very dangerous path by mixing this girl with Navy life. Based on the "logic" she is using, it is clear she doesn't get it. This isn't about you being able to choose to make that day. It is about what the Navy chooses for you, and that may not be in line with what she wants. It isn't just the wedding. It is birthdays and Christmases and anniversaries and maybe even the birth of your own child, not to mention vacations and celebrations and family moments. You *will* miss those things. If she can't handle the uncertainty about the wedding, or needing to adjust her wedding plans, then she will not be able to handle those things. Do yourself a huge favor, have a no bullshitting or sugar-coating talk with her about what it will be like, and get it figured out now so you know if she is compatable with the Navy life. If she isn't, don't stick your head in the sand. Ditch the girl, or ditch the Navy. It really sounds like combining the 2 will be disasterous.
I can't tell if she is the one suggesting you go SWO because it might allow for better planning, or if that is what you have come up with in response to her "one day" logic. Either way, any girl who would encourage you to--or even do anything short of beg you not to-- give up your dream to better accommidate a party is not worth giving up anything at all for.