סימן קסא סעיף יב
לֹא תֹאחַז בָּהּ חֲבֶרְתָּהּ בִּשְׁעַת טְבִילָה, לְפִי שֶׁלֹּא יָבוֹאוּ הַמַּיִם בִּמְקוֹם הָאֲחִיזָה. וּבִשְׁעַת הַדְּחָק, תַּטְבִּיל הָאִשָּׁה, שֶׁהִיא רוֹצָה לֶאֱחוֹז אוֹתָהּ, תְּחִלָּה יָדֶיהָ בַּמִּקְוֶה, וְאַחַר כָּךְ תֹּאחַז אוֹתָהּ, לֹא בְכֹחַ וּבְדִבּוּק חָזָק. אֶלָּא בְּדִבּוּק בֵּינוֹנִי כְּדֶרֶךְ כָּל אָדָם.
Another woman should not hold her during the immersion, because the water will not penetrate to the place within her grasp. In case of emergency, the woman who must hold her should first dip her own hands into the mikvah,8Wetting the hands in other water does not help. Ramah 120. Even if she wet her hands in the mikvah, and took her hands out of the mikvah and grasped her friend’s arm outside the mikvah, it does not help, and is considered a chatsitsah— Levush and Sidrei Taharah. However, the Gra says all water is valid, and even if she grasps her outside the mikvah, and even if she grasps her tightly, it is still valid. Taz says it need not be mikvah water, but he maintains it does not help if she holds her with a tight grip. and afterward hold her. She should not hold her tightly with a strong grip, but with a moderate grip9This is done only in case of emergency, for we are not all experts to differentiate between an average grip and a strong one. (see Sidrei Taharah) that people usually use.
תנא דבי אליהו כל השונה הלכות בכל יום מובטח לו שהוא בן העולם הבא שנאמר הליכות עולם לו אל תקרי הליכות אלא הלכות (נדה ע"ג.)