Tzipporah returns to Har HaElokim

In the beginning of Yisro:

Now Moses' father in law, Jethro, and his [Moses'] sons and his wife came to Moses, to the desert where he was encamped, to the mountain of God.

ה. וַיָּבֹא יִתְרוֹ חֹתֵן משֶׁה וּבָנָיו וְאִשְׁתּוֹ אֶל משֶׁה אֶל הַמִּדְבָּר אֲשֶׁר הוּא חֹנֶה שָׁם הַר הָאֱלֹהִים:

According to Rashi's interpretation of the relevant pesukim, she also was sent away from Har HaElokim earlier:

So Moses' father in law, Jethro, took Zipporah, Moses' wife, after she had been sent away,		ב. וַיִּקַּח יִתְרוֹ חֹתֵן משֶׁה אֶת צִפֹּרָה אֵשֶׁת משֶׁה אַחַר שִׁלּוּחֶיהָ:
after she had been sent away: When the Holy One, blessed be He, said to him in Midian, “Go, return to Egypt” (Exod. 4: 19), “and Moses took his wife and his sons, etc.” (Exod. 4:20), and Aaron went forth “and met him on the mount of God” (Exod. 4:27), he [Aaron] said to him [Moses], “Who are these?” He [Moses] replied, “This is my wife, whom I married in Midian, and these are my sons.” "And where are you taking them?" he [Aaron] asked. “To Egypt,” he replied. He [Aaron] retorted, “We are suffering with the first ones, and you come to add to them?” He [Moses] said to her [Zipporah], “Go home to your father.” She took her two sons and went away. — [from Mechilta]		אחר שלוחיה: כשאמר לו הקב"ה במדין (שמות ד יט) לך שוב מצרימה, (שם כ) ויקח משה את אשתו ואת בניו גו' ויצא אהרן לקראתו, (שם כז) ויפגשהו בהר הא-להים. אמר לו מי הם הללו. אמר לו זו היא אשתי שנשאתי במדין ואלו בני. אמר לו והיכן אתה מוליכן. אמר לו למצרים. אמר לו על הראשונים אנו מצטערים ואתה בא להוסיף עליהם. אמר לה לכי אל בית אביך, נטלה שני בניה והלכה לה:

This is based on logic and juxtaposition. Moshe was staying with his in-law Yisro at that point, tending sheep. He encountered the burning bush on Har HaElokim. (Shemot 3:1). And he is given the sign that in the future, when they leave Egypt, they will worship Hashem on that mountain (Shemot 3:12). Which is Har Sinai and which they indeed do (see Shemot 24:4-5). Hence the name Har HaElokim. He is told to leave for Egypt. He puts Tziporah and her sons on the donkey (Shemot 4:20), with it unclear whether to Midian or to Egypt (presumably to Egypt, thus the following incident with Chatan Damim). And Aharon meets him on Har HaElokim (Shemot 4:27):

The Lord said to Aaron, "Go toward Moses, to the desert." So he went and met him on the mount of God, and he kissed him.

כז. וַיֹּאמֶר יְהֹוָה אֶל אַהֲרֹן לֵךְ לִקְרַאת משֶׁה הַמִּדְבָּרָה וַיֵּלֶךְ וַיִּפְגְּשֵׁהוּ בְּהַר הָאֱלֹהִים וַיִּשַּׁק לוֹ:

And thereafter it is just Moshe and Aharon. So it stands to reason that there, at Har HaElokim, is where she took her leave. And so it is fitting that here is where she returns, after the interlude.

Of course, one can explain otherwise...