Toxic relationship

Sorry for the long story... My cousin and I are only 5 days apart in age and have grown up together our whole lives. We’ve been neighbors and spent our entire childhood and adulthood together. However, we often butt heads. She’s a very manipulative and mean person. She’s competitive and wants to be the best and first for everything. She told our family she wants to “beat me” and get pregnant first even tho she knows I have PCOS and have been trying for a year. She ended up getting pregnant after knowing her boyfriend for 4 months and he’s verbally and sometimes physically abusive. She’s constantly trying to make me “jealous” of their relationship. I’ve been with my SO for 3 years and we have a very good relationship. I did everything for her. I threw her baby shower, her gender reveal, went to appointments with her, got her whatever she needed but she’s still rude. I usually just ignore her or play along with her games but she did something yesterday that hurt me deeply. I’ve completely changed my lifestyle and lost 50 lbs and toned up. I’m not gonna lie, I look great 👍🏼. She had her baby 6 months ago and for the first time in our lives she weighs ALOT more than me. I have never said anything about her weight cause I KNOW she just had her baby and she’s busy and stressed and there’s no reason to be ashamed. Anyways, yesterday her mom had the baby and She wanted to come over. I told her I was going to the gym but she was welcome to come if she wants. She said “no, I have better things to do. You think you’re so great cause you lost weight but you’ve never been pregnant or had a baby so you don’t know what it’s like.” I was so caught off guard and hurt because she KNOWS my pain with infertility. I haven’t talked to her since. How do I go about dealing with her and this? She’s family so it’s hard to cut her off. I’m so hurt.