Meghan’s exact phrasing was this;
“To my understanding, you can't ever wear the same colour as Her Majesty if there's a group event, but then you also shouldn't be wearing the same colour as one of the other, more senior members of the family. “
She says “you can’t ever wear the same colour as Her Majesty”.
She doesn’t say “I couldn’t ever wear the same colour as Her Majesty.”
From this particular use of her language, I take her “you” to mean the collective “you”. Or “one”, if you will.
She also begins “To my understanding”. It sounds as though she guessed this or perhaps Harry erroneously told her this was the case.
She does not say “I was told”.
So when she says, with an instructive / informative phrase “…you can’t ever wear the same colour as Her Majesty”, this is not correct information.
There are several easily available photos of royal women of various levels of seniority wearing the same colour as the the Queen. This is who she is referring to as “Her Majesty”.