Sure there may not be a great wat to measure personality I guess. And I guess the 80% number who knows about how accurate that number is actually. But whether it is 62%, 71% or 80% I think we can all agree that your life experiences up to age 8 have a huge effect on how you will turn out for the rest of your life.
Oh certainly, there is psych research going back a billion years showing the importance of upbringing.
It is quite important though (as you mentioned your friend is a therapist) to understand the terminology and what is actually being stated. You are talking more here about schemas (if you buy into schemas), but it seems to me that schema's are extremely important in personality disorders (schemas are the, mental shortcuts that we develop in order to understand the world), so with personality disordered individuals (such as me) those shortcuts are adaptive to bad situations, the child does what it can to survive, but become maladaptive in the later world.
This applies to SA as well, of course, schemas about how we will be treated by others maintain SA, but they are especially important in individuals with PD. Why? Because unless they are recognised as schemas, any therapeutic effort will fall short (CBT etc, does little to address schemas). Your therapist friend needs to understand this, since confusing this stuff, and the psychological definition of "personality" with the layman definition of personality (they are different), would result in different therapies and different ideas about outcome.
for example, someone with SA isn't usually suffering from a personality disorder, they will probably respond quite well to standard therapeutic approaches. Someone with a personality disorder less so. But if your therapist friend is confusing "personality" here, she is mistakenly assuming a lower response rate than is actually the case.
She is also very badly nocebo
'ing you into thinking therapy might not work on you. A therapist shouldn't do that, very bad idea.
One of the worst aspects of this place is it acts as a giant nocebo factory for SA sufferers, since everyone basically ****s on therapies, often when they haven't even properly done the therapies (see people bad mouthing exposure when they didn't even do it properly), creating a giant nocebo echo chamber, because stating stuff doesn't work enables avoidance, which is what people with anxiety desperately want to do.