What did Rachel mean when she stated that Hashem had judged her...?
Rashi: She meant that Hashem had initially judged her and found her guilty (which is why He withheld children from her), and had now judged her favorably 1 and given her a son (via her maidservant).
Seforno: She acknowledged Hashem's righteousness in withholding from her children, and thanked Him for giving her a son 'a staff to guide her and a shovel to bury her'. 2
Targum Yonasan: He had now judged her mercifully, accepted her Tefilos and given her a son.
Rashi (in Divrei Hayamim 2:13): If Le'ah will be proud of her son Betzalel, who will build the Mishkan, he will need to join forces with one of the sons of Dan - See Shemos 38:23; and if Shlomoh, my sister's son will build the Beis-Hamikdash, he will have to join forces with the sons of Dan and Naftali.
See Yevamos, 65b).
Why did Rachel and Le'ah refer to the children of Bilhah and Zilpah as sons, and not Avadim?
Seforno: Because they set their slaves Bilhah and Zilpah free when they offered them to Yakov. 1
רש"י: דנני אלוקים- דנני וחייבני וזכני: למה לא פירש שזה מלשון דין [-עונש] כמו בכל מקום?
גור אריה: לא היה כאן דין אלא זכות בלבד.