Midrashim says that the basket in which Moshe Rabbeinu was there was far away from batya. She reached our her hands which became elongated.
How far exactly was the basket away from Batya?
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Megillah 15b records an opinion that it was extended 60 amos:
וכמה אמר רבי ירמיה שתי אמות היה והעמידו על שתים עשרה ואמרי לה על שש עשרה ואמרי לה על עשרים וארבע במתניתא תנא על ששים וכן אתה מוצא באמתה של בת פרעה וכן אתה מוצא בשיני רשעים דכתיב (תהלים ג, ח) שיני רשעים שברת ואמר ריש לקיש אל תקרי שברת אלא שריבבת רבה בר עופרן אמר משום ר"א ששמע מרבו ורבו מרבו מאתים
How long [was Achashveirosh's scepter extended to Esther]? R' Yirmiya said, it was two amos, and it stood at twelve. Others say, at sixteen. Others say, at twenty-four. In a Braisa it was taught, at sixty; and so do you find with the arm of the daughter of Paroh, and so do you find with the teeth of the wicked [i.e. Og - see Berachos 54b, and Rashi here], as it is written (Tehillim 3:8), "The teeth of the wicked have you broken," and Reish Lakish said, do not read "have you broken" (שברת), but rather "have you enlarged" (שריבבת). Rabbah bar Ufran said in the name of R' Eliezer, who heard from his teacher, and his teacher from his teacher, two hundred.
According to the Braisa cited, Bisya's arm extended to sixty amos, just like Achashveirosh's scepter and Og's teeth. It's unclear to me whether the other opinions agree that they were all equal and only argue regarding the length, or if they all agree that Bisya's arm grew sixty amos, and they only argue regarding Achashveirosh's scepter.
It's a Midrash. Take it as you wish, whether literally or metaphorically. Note that sixty is often used in Chazal as an exaggeration.