Hi! Apologies for the delay in my reply.
This is an interesting question.
From my limited research and some base knowledge I got from talking to friends, modern Egyptians tend to speak their own dialect of Arabic if I’m not mistaken, so if your character is in the modern era, they would probably speak that. If she’s in an ancient era, she would speak one of these depending on the time period.
It’s a little difficult to integrate nonlatin languages into an English narrative, so I think your best bet is to look up what the spoken language sounds like (youtube would be a good resource here) and describe what it sounds like while leaving the actual dialogue in English. Listen to how the vowels are drawn out, what letters/sounds have more emphasis, etc. and describe that to make it clear they’re not speaking English.
That said, you can also put a certain amount of trust in your readers to put two and two together and realize that native Egyptians, modern or ancient, wouldn’t likely be speaking English.
I hope this was helpful