Caring mother or a little overbearing?

Everytime I do something my mom doesn't approve of or agrees with, she gets upset. It's really unnerving because I'm constantly having to explain my decisions to her. I love her so I don't want to disappoint her. But when I try to explain this to her and how her reactions to things causes strain in our relationship, she disagrees. She's in denial of how her condescending responses make me feel. I understand why she wouldn't agree with somethings I do (like going to visit my bf and his family for 6 days) but she never tries to understand my decisions. She just says I'm hardheaded or selfish, all because I'm not doing what she thinks I should do. What do you think about it and what should I do? I'm 21 btw and I'm about graduate from college this May. Another thing is that my mom raised my sister and I as a single mother.she devoted so much to us and now that my sis and I are grown, it's just her now. Sometimes I feel like she blames us because she dedicated her life to making us happy and now in a sense we don't 'need' her like we once did. In that she has to reevaluate her life and where she wants it to go from here.