I am so sorry you had a bad experience with petco. Don't think you are a bad mommy! She is still young and will get used to it. I didn't take any of mine to my groomer until they were around 6-7 months old, so I would have time to get them used to brushing and bathing etc. My Yorkie was a lot like your when she was young, she would bite at the brush wiggle all around and basically, try to get me to stop, in other words, she kept trying to break ME!! LOL. I just kept doing little bits at a time, every day, even if it was only clipping on nail, or running the brush down her back one time. She really didn't start to calm down with it until about 7 months, and now at almost 3 years old, she is a dream to groom, she loves to be brushed, she almost passes out when I brush her now, she acts like she is a queen who deserves her spa time, lol
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If you can find a groomer that you can go and watch while they do it, it may be a much better experience for you and her. I wouldn't take her to petco again or any of the super pet chains, you just never know. It sounds like the person doing it didn't have enough experience to know how to handle a puppy and a small one at that.
You are not alone and not a bad mommy, just keep on with the brushing and daily grooming at home, have patience, it WILL get better.
