Jealous sister-in-law

My sister-in-law is in constant competition with me & is so insecure it bothers me so much. I am 2 years older than her & have tried to be there for her as a true sister. Whenever she needs advice she comes to me & I give it to her. I remember her special days & cheer her on when she reaches a special milestone in her life. I’ve been there for her highschool grad, her college grad, her first day at a “big girl” job & countless other little occasions. I have never been fake about my happiness for her; I have always been genuinely happy for her.

When her brother & I got engaged 6 years ago... She never congratulated us. When we got married 5 years ago she made the day all about her. She kept prancing around telling our family how many compliments she got & on top of that she & her boyfriend made things official on that day & instead of being happy for me & her brother she made the day all about her. When my husband & I found out we were expecting we took the time to tell our family first before posting anything on social media. When it was time to share our news with my sister-in-law (she was in college at the time) she was telling us about her stressful day at school & never once extended a congratulatory word. And finally when my daughter was born she posted a picture of my newborn & said “I’m an aunt”. Again reflecting all attention back to her... She never congratulated us about that either.

I’m not bitter or angry... just bothered that she has never been happy for me. It’s not like I’ve kept tabs it’s just become so apparent in the way she’s been treating me. There’s definitely a pattern here. What are you thoughts on why she’s treating me this way & any solutions? Anyone been through something similar? Thank you!