Or HaChaim on Genesis 30:3/אור החיים על בראשית ל׳:ג׳

1 ותאמר הנה אמתי, She said: "here is my bondwoman, etc." She was careful to say: "my bondwoman Bilhah," before mentioning that Jacob should sleep with her, instead of saying: "sleep with my bondwoman Bilhah," as Sarai had done at the time (Genesis 16,2). I have explained there that Rachel did not mean for Bilhah to be still called a bondwoman after she had slept with Jacob. She gave Bilhah to Jacob to become a wife to him; any sons of her should be free men. Leah acted similarly when giving her bondwoman Zilpah to sleep with Jacob.

2If we find that even Sarai did use the term "wife" in connection with Hagar (Genesis 16,3), she countermanded such an interpretation by saying that she should be a wife only vis-a-vis Abraham. She was to remain a slave-woman vis-a-vis herself. Compare my commentary there.

3If you were to point out that we find Bilhah described as a bondwoman even after she had slept with Jacob (30,7) and already bore him a second son, this simply means that she used to be Rachel's bondwoman. The Torah there was also interested in pointing out that the matriarchs attributed such righteousness to their husbands and it is certain that the Torah did not need to be afraid that someone would misunderstand having previously outlined what Rachel had in mind (compare what we have written in Genesis 37,2).