How Do I Deal With This?

I started a new job in August.. I got into the routine very quickly, I’m happy. There’s a girl who started 2 weeks before me. She’s fine, she wouldn’t be my cup of tea but we chit chat. She was very helpful at the start, she showed me the ropes and I was thankful. Now, it’s a different story. I feel as though she’s ‘too’ helpful. When I’m serving a customer, she’ll come over and butt in. She won’t really leave me to do it by myself. I’m trying to deal with a customer while she’s asking if they want a bag, a receipt and what not. It confuses me, I like to carry out tasks on my own because it’s less stressful for me. She would also tell me to hang clothes a certain way, even though I’ve been told and shown before on how to do it. She seems like she has an answer for everything, kinda has a problem with anything I say. I always get the feeling that she’s watching me doing things, like she’s ready to prance on me. It’s embarrassing, I feel so humiliated if she calls me out in front of our coworkers. One of our colleagues asked one of us to stay back for a few minutes to help close up and she just made the excuse that her mom was ‘waiting’ for her and she had to leave. Therefore, it was me who had to stay behind. Overall, she just makes it difficult for me to do my job. I really don’t want to get my manager involved, or even confront her. I’m not the confrontational type. I can’t fathom the fact that she’s been there a couple weeks prior to me starting and she somehow rules the roost. I’m just looking for ways to avoid this repeatedly happening.