From what you've written, it looks to me like it's time for some direct and open communication with your wife.
Most of the issues are already on the table. Your wife knows you are poly and always have been, since the beginning of your relationship. You know she is not, or at least that she never has been previously.
She knows you want to develop your relationship with this new love interest. The new lady is interested and on board with the idea. Your wife has said she's not emotionally ready to move ahead.
The question then becomes: what does your wife need in order to become emotionally ready? Perhaps she needs to be better educated on polyamory. Perhaps she needs to do the internal work to address her fears, insecurities, jealousy, or whatever other issues have become obstacles. Whatever her needs are, y'all (the three of you) need to come together to make a plan to overcome the obstacles so you can move forward.
From what I've read here, you've shown respect, honesty and integrity from the beginning. It is not at all unreasonable for you to insist on some forward motion toward having your needs met too. She knew you were poly when she married you.