Rashi says she baked cakes not bread because she was in Niddah. How does this make any sense? We bake bread whenever.
There is a mistake in your lecture of Rashi, the "cakes" are bread, ugot refers to the shape form. Later rashi writes that they eat butter, milk and meat but the bread (& / the cakes) is not mentioned. Why? Because she became Nidda, and the dough became unclean. They were stringent to eat "Chulin Betahara" according to Rashi. This is not a strict obligation from Halachic point of view. Nowadays, we have problem with dead uncleaness, or Tum'at Erets Haamim, we cannot be clean.
About the "Make cakes".
1. The verse:
the word is Ugot.
2. The translation of Onkelos:
the aramic translation is "Gritzin".
3. We found Gritzin in Mishna (Betsa 2, 6):
וְאֵין זוֹקְפִין אֶת הַמְּנוֹרָה בְיוֹם טוֹב, וְאֵין אוֹפִין פִּתִּין גְּרִיצִין אֶלָּא רְקִיקִין. אָמַר רַבָּן גַּמְלִיאֵל, מִימֵיהֶן שֶׁל בֵּית אַבָּא לֹא הָיוּ אוֹפִין פִּתִּין גְּרִיצִין, אֶלָּא רְקִיקִין.
According to Rabban Gamliel, to bake a great quantity of dough is prohibited on Yom Tov because of the great effort needed. This great quantity (גריצין gritzin) of dough (Pat, pitin). Rashi says that Pitin Gritzin are thick loaf of bread, Tosfot Betsa 22b says large loaf of bread.
So the translation "Ugot" ="gritzin" = "cake" may be a consequence of the expression Ugot nowadays in modern Hebrew and doesn't come from the traditional lecture of the verse.