Your analogy is incorrect as it does not apply to what happened to Leah. Leah did not attempt to "take away" a son from Rachel and it was thanks to Hashem who had done this. Rav Hirsch points out that with each of the three previous sons she recognized an increasing connection to her husband. In fact, Rav Hirsch says
It is accordingly, highly significant that at Levi, it is not she, but
he who expresses this in giving the baby its name. ... so that, when
the fourth son was born, Yehudah, she no longer had to welcome it as a
means of progress in her husband's love towards her, which she now
fully possessed, but could simply enjoy her baby purely for its own
sake. She accordingly pronounced the words of a happy mother "This
time I can thank Hashem, just for His gift itself" and called the
Thus we see it was not taken away from Rachel, but an acknowledgement of the goodness of Hashem.
Additionally, she could have considered him the fourth child of the six that she had been alloted. That is, the maidservants had not yet been given to Yaakov as wives and might not be part of the count. According to Rashi, who counts all four, Rachel could also have had four and each of the maidservants two. Thus, the acknowledgement did not "take away" from Rachel.
Indeed, When her final child was born (Dinah), Leah prayed that it be a girl and that Rachel have a boy (Yosef). The medrash says that originally, Dinah was supposed to be another boy and Leah's prayer changed the event so that she had a girl and Rachel could have two boys.
Thanks to @DanF for pointing out that Rachel did not feel as the analogy might have it either.
Within the "mix" keep in mind that when the Torah says that she was
"jealous" of Leah, it was a "positive" jealousy (see Rash"i on that
verse). She was jealous that G-d answered Leah's prayers, and realized
that she had to try harder. She wasn't hurt that Leah had all those
children. If anything, we see how Rachel always tried to appease her
older sister, even in a situation where, perhaps, Leah was acting
"mean". In short, to say or imply that Le'ah was rubbing it in seems
incorrect. – DanF