I am sorry you are getting so much flack, OP, when you have admitted you got a lot wrong. There is nothing wrong in itself in having a new partner, even though that inevitably means your DD will not have your undivided attention. As someone who has survived a VERY rough teenage patch with DD1 (now 20 and we get on very well!), it doesn't sound like the end of the world.
Relationships get strained, it happens. Older teens do not necessarily want to go on holiday with their parent(s), even where there is no step-parent. At 16, DD1 was convinced that any caring, reasonable mother would provide her with her own studio flat (near enough to bring her laundry round, eat at home whenever she wanted etc etc!) - tbh she was so awful to live with I might well have done it if I could have afforded it. I am not saying I am perfect,but there was a whole lot of 'stuff' DD1 was going through which was not due to anything I ever did or said. At times I suggested she choose an adult we both trusted - a teacher, one of the church leaders, a favourite aunt, she could nominate who she wanted - and we sit down with them and get their perspective, but she always refused...
It was a horrible thing that you said, which you fully acknowledge and you understand your own triggers and where it came from. I would make a direct apology for that, explain where it came from in your own life, and acknowledge that wherever it came from, you were wrong to have said it and do not mean it. That you love and miss DD, respect that she probably needs some space, but that you would love her to come home, and are very willing to meet up whenever/ wherever to see her.
Acknowledge that DSS is also at fault, that his father will address that with him (as long as he is going to - if not, that is a problem).
When she is ready to talk, listen. Ask her suggestions for what could improve your relationship, and for the family/house rules. Don't interrupt, don't react. Make notes, summarise what you think she has said to make sure you have understood. Thank her for her suggestions, and ask for time to think about them.
Seriously think about what is possible, practically and emotionally. If she wants a weekly spa day with you, but you can't afford it, think about what you can manage. a weekly mother/daughter coffee date. A monthly mother/daughter day, you set a budget and she chooses what you do together.
What complaints have substance? Is she expected to do more than DSS? In what ways? Does he do less around the house but she gets more support or treats in other ways? Is that still the support/ treats she wants, or has she grown out of them?
What is it she isn't getting enough of, from you, at this stage in her life? Bearing in mind that what she needs and what she wants are not entirely the same, and you are also human and have needs and wants as well. It is reasonable to expect everyone in a family to have all their needs met, and some of their wants. The younger the child the more has to revolve around their needs, of course, and at periods (e.g. exam time) one person's needs may have to be more of a priority for a time.
Good luck. The best advice I ever got was that it was part of my job, as a parent, to model how to put right a mistake. Not that we should make deliberate mistakes! But, being human, we are going to make them, and the way we handle them is more important than trying (and failing) to be perfect.