"Her impurity/defilement was found in her lower parts." This verse is speaking of the Nation of Israel as a whole- referred to in the feminine - Receiving The Torah From The Infinite One.
This verse has many meanings; beginning with the literal.
The Previous Chief Rabbis of Tunisia HaGaon Rabbi Yosseph Gez writes in the name of Chaza'l (Our Sages May their remembrance be a blessing) that the reason the very first Strike against Egypt was Blood was because the Egyptians did not allow The Women of Israel to dip in pure waters to purify from the natural cycle to be able to be with their husbands in purity & conceive in purity. God's payback therefore to this "unrepented" evil- is as always the most perfect which is exactly measure for measure. (& a Good example of how the Torah speaks cleanly & content matures as you do, as you continue your studies).
If we may attempt now on a level of Deroosh - A level to dive deeper into the verse- extract the meanings - on a metaphorical level- The Lowest parts that pertain to Her - The Nation of Israel- is The Torah itself - but even lower is The Aleph Bet. (Being lowly is actually praise; humility - the key to the best life.)
The Torah is compared to water (Bavli Taanit 7a)- for just like water originates in the highest places and flows down to the lowest levels - The Torah Wisdom Lights/Guides of God originated in the highest heavens, & descended down to this earth.
But The Aleph Bet are even lower than that. How? Abraham & Sarah call the Aleph Bet Avaniim - Stones- if you throw a stone into the ocean- the stone will descend & reach the very bottom of the ocean floor. (-AE) The Aleph Bet are The lowest things literally in existence- on the very ocean floor of reality. Originated in the highest places- The Crown of God (O.R.A.)- & fell to the lowest places- meant for kids first beginning to speak/make sounds.
"The defilement of her lowest parts" means the corruption of The Torah & Aleph Bet in this world. Translating The Torah into every other language- LEAVING GOD'S SYMBOLS for man made scribbles & we lose nearly everything. All that is left are stories. The Tanakh was rearranged, and 4 books split into 2, and prakim foreign breaks to the Text were inserted, & The Script was changed from Ktav Ashurith into misshapen uncrowned aleph bet & The things that are supposed to be the lowest parts- the Torah & Aleph Bet reaching children- has been prevented from doing so.
So instead of her defilement at her lowest parts - What is the flip-side?
"Her purity/clarity/holiness was at her lowest parts- The Pristine Torah with The Real Aleph Bet - exactly as given on sinai. NOW you can begin to experience the Depths of Infinity- There is no creator designer like HaShem - To quote Hannah the prophetess - the mother of Shemooel The Prophet. (Bavli Berachot)