Berit, I think you should rely on your parental instincts.  Personally, I believe that the best way to deal with Louise's concerns is to remain as open with your daughter as possible.  My son may not have understood exactly what a psychiatrist was, but that was OK:  he knew this was a person who was going to talk to him for quite a while, ask a lot of questions, and try to see if he could figure out how my son thinks.  Not that anyone can ever really KNOW how someone else thinks, but some people are trained to try.  My son could grasp all of that.  At age 7.

My son, like your daughter, is very young in some ways, and very grown up in others.  I've learned not to ever assume that there is something he cannot grasp.  We talk about everything.  If it becomes apparent a concept is beyong him, I just hug him, tell him it's OK, not to worry about it, he'll figure out what I was talking about when he's ready.

I know that everyone has different experiences with special education and the evaluation process, and we are probably unusually fortunate, but my son has seen nothing but positives come out of his tentative diagnosis.  He is so much happier now that he "knows," and now that the adults around him "know."  He does not see Aspergers as a negative, and he never explains it to anyone else as a negative.  He knows it is what makes him different, but he also knows it is his gift, and the reason he can think such amazing things.

As he gets older and kids around him change, maybe he will view all this differently.  But, I hope not.  We are in a district known for it's excellent special education and acceptance of diversity.  He can choose places like that his whole life, as far as I can tell, and write off those who can't accept him as the exceptions.  I will prepare him for that, when the time comes for him to understand the broader world isn't always like our lovely little pocket.

He recently got put on a soccer team that was completely wrong for him.  I had a few pretty bad days worrying about how that happened and if my trust in the other adults around me had been missplaced, actually.  But, my son trusts that we will fix it.  He accepts that we might not, but he trusts that we will.  And, it turns out, my worries were wrong and it was a mistake, so it probably will get fixed.  This is my son's experience in life; people give him what he needs.  I know, there are teens here who think that I shouldn't be keeping my child from the wolves, because it isn't realistic, but how can a mom NOT protect her child?  He needs this, now, while his wings grow.  And they ARE growing, in his own space and his own time.  He is, at age 9, starting to acquire a lot of independence and responsibility ... I am so proud of him!

Lol, sorry, I digress ...

I found the diagnosis to be a good thing.  I am sorry that Louise had a bad experience.  But, as I said, I think that her concerns can be dealt with.

One thing I do recommend, is asking upfront what all the downsides are to the process and having notations in his file.  I found the professionals I was working with to be pretty blunt about it, but the clincher was discovering that parents in my district are trying to get perfectly normal kids classed as special ed so they get more time on tests, which gives them an edge in getting better test results.  I thought that was way too funny.  BUT, the long term point is, the entire discussion gave me very good insight into how my son would be viewed in this district, and what the long term pro's and con's might be.  Getting something put in someone's permanent file always takes a lot of thought.

I have found I am actually choosing, mostly by inaction, not to formalize the diagnosis, however.  I don't seem to need a doctor's opinion to get my child services in this district, and I guess I feel like I have more flexibility for the future by not having that finality in my son's records.  That's why you'll see me often use the word "tentative" when I refer to my son's diagnosis.  We only have the evaluations made by the school.

Personally, I found the evaluation process educational by itself.  Stressful, yes, but very insightful.

OK, got to get back to work.  Hope something in here was helpful!