Parenting a dependant 20 year old, when they are rude, is difficult and painful.
You must feel so sad that she won't confide in you, you are deprived of feeling genuine joy and meeting her lovely boyfriend, and she treats you terribly - even though she is a dependant and needs to be housed by you for the holidays.
It's such a hard position to be in. If she was a summer lodger you would easily cut her off or chuck her out.
Is she coming home for Easter?
Are there siblings?
Detachment is the key. She is an adult and can be treated as such. You might choose to offer her a bed for the holidays but you need not flex your life to accommodate a rude daughter. Tough love. There are consequences to everything. She can see results of her actions and knows when she is sweet she gets help,and when she screams she can upset you.
Don't expect to be in her good books, nor to have a great relationship at the moment. She controls what she eats, who meets her boyfriend, and how she interacts with you. It might be a disorder that means she is difficult. However, she is capable of living independnatly and she can't control you.
Be cool. Extend kindness that you can but cease trying to have a relationship. Show her that there are consequences and so be detached from her damaging ways.
Make no excuses and do what you want. Lifts if you fancy a drive, but not if you don't. Use your home as you wish and not in a way to suit her. Be even handed and consistent. She might not consider you someone to respect right now (she behaves badly) so as she is now an adult you need not pander to her moods.
It's a privilege for her to be housed with you,not a right.
She can't control your feelings. Take it easy on yourself and show her you love yourself. This is important. Show your daughter, pointedly, that you treat yourself nicely. Tough love means she is not enabled to be hurtful to you followed by you being desperate to have a warm relationship with her. She can't just take stuff. Tell her that is theft. She is selfish and immature if she doesn't see that she needs your support. You could warn her that if you feel her disdain is apparent during the Easter stay that she should consider her options for the summer hols? She is obviously not happy with the support you provide. What are her options? I suppose she could stay in her university town.
My heart goes out to you. Did she go into teenage-hood as a nice girl?