If a new acquaintance acts like she doesn't like you some of the time, she probably doesn't like you all of the time. What you're likely seeing is thinly veiled hostility, and it comes out at times when she can no longer hide it.
However, she still keeps you in her life, because, at the moment, you serve a purpose. Perhaps she's asked you to drive her children to school in the morning. Or, you might have a wider circle of friends and she'd like to get to know them. So she needs to keep you in the picture until she can accomplish her mission. Or, maybe you work with someone who fits this description. She can't show her true feelings, because everyone else in the office likes you. So she must mask them. You notice the anger and resentment only when her mask slips.
People who relate well to others do not act this way. They are open and approachable, and aren't subject to these mood swings.
This moody person is not a true friend and she never will be. In fact, she may have a serious personality disorder, such as malignant narcissism. If that's the case, you certainly don't want to waste your time with her. For one, it's a losing battle because you can never really please a narcissist, nor can you possibly live up to their ever-changing and unrealistic standards of what constitutes perfection. Also, once such an envious and malicious person gains access to your life, she create a lot of drama, which can take a long time to straighten out, and you may never be able to completely repair the damage.
Malignant narcissists are dangerous. My best advice is to learn all you can about this destructive personality disorder, and watch closely if you suspect someone is hiding their real personality behind a pretty facade.
Pixabay image top by Nemo