I'm so sorry @Purplebiscuitwithsprinkles that your friend has been subject to this and feels she has had to change career.
I absolutely love our SENDCo and I cried at the end of term as my DS is going into secondary education in September and everyone, especially our wonderful SENDCo has supported us all so much.
I am not surprised your friend experienced what she has though, because we've seen it ourselves. When my other half came back from an SEN event he took our DS to, and had seen some other parents, he said "I didn't realise how much some parents hate Mrs X".
I like to think we had a good working partnership with our SENDCo and school, but I think that's the crux of it. You have to work with the school and can't expect them to do it on their own. We implemented the same things at home they were using in school and were under no misconceptions of how very difficult it was. A lot of parents are reasonable like us I think, but there seem to be even more that aren't. I've listened to them and I don't know what to say, because I know it won't make any difference.
Maybe it's a wider issue as it often seems to me that people expect everyone else to do things for them, be it school, the government, the police, or whoever without any work on their side. I also think we only ever hear about bad experiences in the media, so the perception of what people are going into is skewed. In truth a lot of the time you've already had a fight to get to where you are so that doesn't help.
Please let your friend know she is appreciated and there are many many parents who do know how hard she works. I'm really sorry she's had to leave her profession and hope she has success in her new venture.