My mom is worrying me and upsetting me?

Okay well I'm a 15 year old girl and my mother is 50. Now she may be going through menopause but I'm not sure, but she just worries me. Like she's an infection's disease doctor so she has a lot of stress. Don't get me wrong I love her and she's the best mom and loves me too. But what worries me is how she over re act's over small things which makes me stressed out too. She's just always upset half the time, and always puts herself down. She also tends not to listen to me. And when I try to make her feel better it just makes it worse. And she says things to me that are horrible..and she doesn't mean them..but I just wish..she would relax and be happy, because I try to be as best as I can, but I just can't take it anymore..and if I try talking about it with her she just seems to get offended, no matter how sweet I am...trust me I don't yell at her I talk to her in a nice manner. It's just really frustrating and I just feel even if I get counseling she'll just get mad and start saying "well if I'm such a bad mom why don't you find your self another mother" she said that once to me when I thanked another mom who helped me back stage at my dance recital, and that only was because my mom was busy helping with the little dancers. I just don't know what to do and I'm just....upset =(