I partially agree with Dev, in that it is your partner's choice how fast to move with your new partner. She is NOT in a relationship with her; you are. She doesn't ever have to meet her. You have to trust her choices.
There is the risk that if she chooses to uninvolve herself from a part of your life, that she might find herself "out of the loop," when it comes to major parts of your life, feeling as if she's excluded- BUT THAT WAS HER CHOICE. And she may be totally okay with not knowing that half of your life.
The red flag, for me, is that you say the reason for this is not a lack of interest, but because she is "struggling to get past her fears I will fall in love with someone else." This speaks to a "don't ask, don't tell," relationship, and usually indicates major issues with the relationship. I can totally understand your new girlfriend being wary of your partner's insecurities with poly as a whole.
I have gotten myself in a DaDt relationship, and, fair or not, I don't think I would ever put myself in a situation where I couldn't meet both partners up front. Burned too badly before, and can't handle the ensuing drama that could result and me already in love with the man/woman.