Your Dd said im never there for her, I have my priorities elsewhere and would prefer to shop that support her when she needs me, she’d ‘never felt so low’ and we still couldn’t come over. She said she never asks anything of us of this nature and that she was clearly desperate and alone, and we failed her. We apparently only give her money, not emotional support. The list of accusations went on and on: mostly that we were selfish for going shopping when she needed us
She's right, sorry. Given that she doesn't ask for your help every week at short notice my parents would have treated my breakup as urgent and important, a family emergency, and if I'd asked they would have come straight over the next day. To most people a 35 minute journey is nothing. Missing a shopping trip for curtains is nothing it could have waited a week.
You and your husband are extremely rigid and inflexible. What goes around comes around. I am in my 50s, about to move hell and water to visit my own father (who is elderly) and has been unwell and needs some support. (Sharing visits with my DBro and DSis) I have had a few days' notice but it's a 300 mile journey, and I work fulltime, and am busy too. In future I can't see your DD making much effort for you.
when my 18 year old visits me, he has the manners to class himself as a "guest."
He shouldn't. He is your son and he should take a lot for granted.
my daughter just had a difficult temperament.
No, she had a temperament that you don't understand. So far the limitations you describe are in you and your DH, not in her.
I love my children very much, I am not cold hearted.
In your own way I am sure you do. But it's not about whether you love her in theory - it's whether you are willing to put yourself out to meet her emotional needs. Which you are not, and by the sound of things you never have been. It doesn't sound as if you even understand what those needs might be.
That doesn’t mean I can’t see that she’s difficult and dramatic at times, her reactions are extreme.
No, her reactions are just normal. Ordinary. Yours are out of whack.
DH and I can sometimes see why her relationships break down.
Her relationships might break down because she has grown up without good role models for managing relationship problems and especially conflict. Or they might break down simply because, well, normal life isn't always neat and tidy like yours. Most families help each other through troubles, emotionally and practically and not just with cash.
She didn’t calmly tell us she was upset we hadn’t visited,
But she wasn't "upset you hadn't visited". She was devastated because once again you had failed to step up when she needed you. She doesn't feel calm, why should she sound calm? Are you unable to cope with emotional expression? Is calm and neutral and polite the only kind of communication you can handle?