וְכִֽעֲסַ֤תָּה צָֽרָתָהּ֙ גַּם־כַּ֔עַס בַּעֲב֖וּר הַרְּעִמָ֑הּ כִּֽי־סָגַ֥ר יְהוָ֖ה בְּעַ֥ד רַחְמָֽהּ׃
E la sua rivale irritava, per farla agitare, perché l'Eterno aveva chiuso il suo grembo.
Metzudat David on I Samuel
And her rival would anger her: Peninah, her rival wife, would anger her with words.
Radak on I Samuel
Her rival (tzarah): Peninah, who was a tribulation (tzarah) to her. And likewise, all two wives [married] to the same man are called tribulations (tzarot), since they are generally each other's enemies. And likewise in the Mishnah (Yevamot 1), "exempt their tzarot."