Isn't it Kuh-ching, not Koo-ching? Kuh as in "cut," but without the t, and ching as in kaching, that money sound.
I mean, Keqing is clearly a Chinese-based character (Liyue, duh), so figuring her name requires delving into Chinese. Chinese is a character-based system, so the first step is to separate the name by syllable, in which case it becomes Ke and Qing.
Chinese has a "pinyin" system that accompanies their characters. It's pretty much never used in serious Chinese, just as a learning tool. It mostly uses the english alphabet, except v is replaced with a different character. That's a minor detail, though - we just need to know that due to pinyin, we can actually translate the English name directly into it's Chinese version.
In Chinese pinyin, "e" makes more of an "uh" sound. "K" is always a hard k sound. So "Ke" sounds like "Kuh."
In Chinese pinyin, Qing can actually be divided further into two subparts, Q- and -ing. "Q" makes a "ch" sound, and "ing" sounds exactly the same as the "ing" suffix in English (running, walking, etc.), so Qing sounds like "ching"
Thus, Keqing sounds like Kuh-ching, not Koo-ching.
Minor nitpick, I know.
And wow, I just dredged up old memories of learning Chinese just to analyze a video game character's name. I have no life.