Awww, congrats, it's awesome to hear that things are going well!
When it comes to openness and judgement, just remember that most people tend to look harshly upon anything new that seems wrong to them, and soften over time when they see it's not so bad. They need to experience it firsthand to get over their prejudices.
Queer people often go through this when they come out to their families -- painful judgement at first, then acceptance over time. My own mom was very distressed when I came out of the closet about my gf being married, and now, a couple of years later, she's totally fine with it and seems to almost see my gf's baby as a surrogate grandkid.
I'm not saying there's an obligation to come out right now, four months is a short amount of time, just something to keep in mind for the future especially if your gf doesn't end up dating anyone else any time soon... being without another partner she can openly acknowledge, staying in the closet indefinitely, while no fun for anyone, would likely be hardest on her in the long run.
Me, 30ish bi female, been doing solo poly for roughly 5 years. Gia, Clay, and Pike, my partners. Davis, ex/friend/"it's complicated." Eric, Gia's husband. Bee, Gia and Eric's toddler.