Was she friends with your sister and her friend before becoming involved with you?

I'm presuming things are serious, since you've brought her in to spend ample time with your entire family? Am I understanding this correctly?

One thing that I do know about being brought into families, where even 1 family member is rude, is that it's important to not wilt nor wither under pressure. Plus, it shows reverence to you to behave cordially enough if being brought into the family. I mean my exh warned me ahead of time to save my kind demeanor if put on the spot. I didn't really need to, but having the green light to not be a total people pleaser was important as his family is very large and can have moments of pure crass.

That said, I worry about the 'dividing the family' comment. It's not up to her to plant seeds of distaste unless your gf was doing something truly horrendous like theft, lies, cheating etc. Sooo...she didn't click like on FB--- ugh. Fb..ugh and she refused to engage in more than crawling into her shell while in the presense of your sister who obviously doesn't like her.

The question is....Do you like her? Isn't this about you, your life and your choices? How often are these family get togethers anyways? Maybe less is more?