Not on Birth Certificate

Ok so first off I'm in a same sex relationship with another female and we have been together for 2 years... we started trying to conceive about 5 months ago and everything has been going great until we switched to a different donor this month and we used a donor contract... the contract has a place for not only the donor and receiver to sign but also for me the partner to sign... we were in a hurry when picking up the sample so the contract has only been signed by the donor and she just blurted it out after the insemination the other night that she didn't want to make me mad but she doesn't want me to sign the contract... her reasoning is that she has no legal rights over our 4 year old son that I conceived before I met her and that it isn't fair to her... I have even brought up the idea of her adopting him in the last and she's kind of blown it off... I feel like I have just been smacked in the face... I have been the one arranging donations and spending countless hours talking to donors and finding the right fit for us only to be told that I can be a parent just not legally... should I feel this way? This has even made me distance myself during the TWW to the point that I feel like I'm already distancing myself from my child that I've helped conceive because I'm afraid of it being ripped away from me and I feel like she's telling me it's not mine like it is hers