Hang in there op 
I suspect this may be more about her age then her family circumstances. But there may be some jealousy involved over your new dp and a fear that you will have less time for her.
I wouldn't tolerate that level of disrespectful language and I would make that clear by turning away, walking away, not engaging and not being suddenly willing and available to give lifts/ do favours/give money etc until she treats you more respectfully.
Teens often take out their frustrations, uncertainties and angst on the people they love the most and while we are there to reassure and support, you need to make it clear that you are not their kicking stool!
Do NOT get drawn in to arguments, petty disputes, or engage in any petty discussions; however infuriated you feel; or it becomes a very negative cycle. By far the better approach is to stay just slightly aloof - while obviously making it clear you love them loads (and saying and showing that a lot) and keeping the important lines of communication open if ever they need to talk - but otherwise just sail slightly above the every day angst. Model cheerfulness, common sense , politeness and positivity without being a Pollyanna. Do things to boost your own mh. And focus on some of your own interests.
And try and do a separate activity with her out of the house which is enjoyable so at least one part of your interaction is positive; even if that is just a drive to pick up a takeaway or have a coffee somewhere.
When my teen DD was at her bolshiest (she is 18 now and is growing out of the worst!) I also encouraged her to take on responsibilities that were slightly outside her comfort level ...so she had something else to occupy her and focus her energy on ...and also it put her in the position where she didn't "know it all" and she had to learn from those more experienced then her ...we did this through a volunteering programme (The Red Cross) and a sports programme (involving horses) but it could be anything ...helping with an aspect of your job ?? Volunteering in the community with the elderly? Fund-raising?
And I found reading 'Untangled' by Lisa Damour very helpful.
Life is very hard for teens and young adults ATM and they are understandably frustrated but it's no good for them if you allow them to cross too many boundaries! Good luck [