相手には when speaking of "two third persons"

Question

I want to clarify my understanding of 相手には in the following sentence...

「人見知りをしない相手には強気なところがあるよな」

It refers to a person that usually acts rather shy around others but scolded one of her acquaintances for his previous behavior. The preceding clause: 「旦那に対して説教をしていた」sounds to me as if it is the 旦那 is being scolded.

What confuses me is 「人見知りをしない相手には」so far I understood 相手 as a person (etc.) different than the doer of an action. In combination with 人見知りをしない I thought of it as "A person the aforementioned shy-person is actually familiar with and therefore not acting bashful".

To cut to the chase I am struggling with the meaning of 相手には in context between two third persons (from the narrator's view).

Answer 1

This 人見知りをしない相手 is "someone who she won't be reserved/shy with". That is, 相手 refers to the person she talks with, but the subject of 人見知りをする is the female person herself. This is an example of adverbial-head relative clauses. Please read this discussion, too.

彼女は彼に人見知りをしない。
She is not shy with him.

　↓

(彼女が)人見知りをしない人
someone who she is not shy with

In other words, the sentence is saying she is an 内弁慶.

Answer 2

相手, unlike, say, 人, specifically denotes the receiver of an action. So while "人見知りをする人" indicates the person being shy toward someone else, "人見知りをする相手" indicates who that someone else is.

In the case of your example sentence, this is the person being scolded in the previous sentence.

The には here has the same meaning as "に対しては".

Using "A" to refer to the scolder, your sentence translates as:

A can be really firm/aggressive towards people she's not shy around, eh?