This is something that she will only learn from experience. Nobody is born as Pollyanna.
she just focuses on the negative and blames others. I don’t know what she’s like this, I always look for the good in things and so does DH.
But you are adults, and she is 12. It's completely developmentally normal for her to lash out and look for other people to blame when she is upset. It will take a lot of time and maturity for her to get to a point of being able to change her emotions. You might as well look at a 2 year old rolling around on the floor screaming and say "DH and I don't do this, I don't know where he gets it from?" I know that's a silly example, but it is genuinely partially developmental - metacognition, which is the executive function involved in being able to think about your feelings and reframe them so you can see them from a different angle, is one of the last executive functions to develop. It's an extremely mature thing to do and comes more in late teenhood/early adulthood.
Until this is well developed, the only real coping skill with emotions is either to externalise them, which is all the screaming/crying/complaining/gnashing of teeth as well as blaming others and making up wild excuses. Or just literally to have lots and lots and lots of repeated and varied experiences of moving through various emotions and coming to a calmer place and realising that nothing catastrophic happened (as a result of the emotion itself). There is also co-regulation, which you know about, and still has a place throughout life, although note that co-regulation is NOT "making someone feel better". It's more about being a calm and sturdy presence or a listening/understanding ear, without necessarily trying to fix or solve or make better.
And there is internalisation, which is bottling things up/funneling it into anxiety, low self esteem, or body-focused behaviours - this is unhealthy. Some externalising is unhealthy as well and it's helpful to have boundaries around what you will accept in this way.
But in general a lot of processing of emotions at this age will be verbal, it doesn't mean that it always will be, just like she stopped throwing rolling-on-the-floor tantrums and started to use her words instead. It's progress, it's just very slow.