It's not about Orna's views but about giving her client relevant information so her client can make an informed decision about whether she is an appropriate therapist for them.
It's not about whether Orna can disregard her feelings, but about whether her client can disregard theirs.
If Christine hadn't already known, she would 100% have found out at some point. That's the context. Going back to your analogy, if your therapist were anti-abortion you might never know, unless you saw them standing outside your local abortion clinic with a placard - at which point I'm sure you would feel aggrieved if they hadn't mentioned they were a pro life activist.
I can imagine a scenario where someone with Christine's history might not feel comfortable with an Israeli therapist. As it turned out I think she saw it as a positive. So she hadn't even disregarded it herself in assessing whether Orna was right for her and Nadine.
I can't remember when, but at some point Orna has also discussed whether her black clients feel she's the right therapist for them.
And she said she might not be the right therapist for that dickhead Sean.
That's being more professional than just taking their money and disregarding what's best for them.