It must be hard having to manage your child's difficulties, your emotions about possible diagnosis and your DH's responses as well!
My DH is the type to just leave it to me and assume that I know what I'm doing which has its good and bad points so, no, he didn't resist the diagnoses. It has given him reason to question his own traits and behaviours and there have been times he's found that quite threatening I think but it's also given him some insight into the fact that his behaviour isn't always that reasonable. Also DD1 was in crisis after falling to pieces on her second day of high school and missing the rest of that year so there was no choice really.
DD1 felt comfortable with her dx from day one. In fact, she recognised her autism when she spent some time in the school's autism unit months before anyone suggested it to me. She says that the dx explained for her why she had always felt on the edge of groups, as if they had another level of communication she was missing out on. She loved the fact that there were other people like her out there and she wasn't alone in feeling a bit odd and left out.
She has just finished sixth form and has a lovely group of friends. Some of them are aware that she has AS, the others just know that she has had a TA to go to for help now and then. None of them seems the slightest bit interested in it, never mind bothered. She chose to include her dx on her UCAS application form so she could apply for some support at uni and she still got five offers, two of which were unconditional.
You know your DD really well and, if she only relied on you, she probably wouldn't need a diagnosis. There's a saying that nobody has Autism when they are on their own in their bedroom. At home, with you, safe and understood, a diagnosis won't make a difference because you will put in everything you can to support her anyway. The assessment reports might give you strategies you hadn't thought of but that's about it.
However, your DD isn't going to spend her life just with you. She needs the people at school, at Brownies, in hospital, etc to understand her and be willing to make adjustments for her too. The dx makes those things easier.
If she has Autism, she also needs to understand herself and her own difficulties. She needs to know the reasons that she finds some things harder than her peers otherwise she might just decide that she's inadequate in some way. My DD2 is beginning to understand that, although facing new situations is hard, that is only because they are new and it's worth persevering because that feeling goes away. Without knowing that AS makes change harder to cope with, she wouldn't understand this and might not be willing to try to overcome it.
If Autism does fit your DD and the professionals agree, you can ask them to discuss it with your DH. There are support groups for parents of children with Autism. Maybe you could find one in your local area to get some support for yourself? Those groups usually have lots of parents whose children don't have a dx in them so don't worry about that.