The terms 'defining' and 'non-defining' are more than a little misleading. They aren't really meant to help ESL students understand. They were designed to confuse English native speaking students and their teachers. The teachers don't really know what they mean but they teach it anyway; the ironic part is that all native speakers already know how to use them.
Now to address your concerns. In the sense grammarians use them, both these examples are defining clauses. You have to view this in context. Imagine that I'm describing this actress. Within the context of my speech, I'm defining which actress I'm talking about. Same with the friend; it's not just any one of my millions of friends, it's the one/one of the ones who is a lawyer.
A better description or one that is maybe easier to grasp/understand is a limiting clause. My comments on the actress/friend are limited to the one's I'm describing. The info I've so far provided to you, that "most people think she is at the peak of her career" and that "he/she is a solicitor" certainly do not define clearly to you just who I mean but the test of a defining/limiting clause is not viewed from the perspective of the listener, rather it is viewed from the view of the speaker.
Putting commas in, in these two cases, will not change the meaning one iota. Some might argue that a defining/limiting clause such as, "who is a solicitor" means that I only have one friend who is a solicitor but that is a real stretch. In some cases, adding commas could change the meaning/nuance.
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