The situation is where the phrase "let " is being used after "have", such that it is being used as a past participle. Such as:
I should have let her know
I should have let her known
You could have let us do yoga
You could have let us done yoga
Which is the correct usage? Are both correct? Also, what language rules does this use (i.e. Why is this the case)? I'm leaning towards using the past participle form rather than the infinitive for the verb, but I'm not sure.
If you don't have a definitive answer, I'm also interested in hearing what you think sounds more natural.