Another interpretation: [she was called Puah] because she would cry out [po'ah] through the Holy Spirit and say: My mother is destined to bear a son who will save Israel.
Miriam Prophesies Her Mother Will Bear a Savior
Yalkut Shimoni on Torah 164:5
דָּבָר אַחֵר, שֶׁהָיְתָה פּוֹעָה בְּרוּחַ הַקֹּדֶשׁ וְאוֹמֶרֶת עֲתִידָה אִמִּי שֶׁתֵּלֵד בֵּן שֶׁמּוֹשִׁיעַ אֶת יִשְׂרָאֵל.