Sibling Rivalry

Hello, I am posting again about a separate issue since I got such a great response from you guys last time.
I have always been very competitive with my sister (and others) and now I feel really guilty about it. I'm just going to be totally 100% honest. I really don't know if these feelings are normal or if I'm just evil. I'm worried I'm a narcissist and that I want my sister to make mistakes so it looks like I'm succeeding. (For some context, I am 23 and she is 20).
Example:
1. She always was always much prettier than me, but she is slightly more overweight than me. Recently, she explained to me that she was on this drastic diet. I really did not like hearing that and I got jealous. I've been sort of dieting for awhile but hers was more extreme. I told her that she didn't need to be on a diet, and that I didn't think she needed to lose weight. (I did not tell her that I thought she could lose a few pounds, I guess because I didn't want her to lose a few pounds ). We went out to eat and she barely ate any carbs, and didn't get pasta like she usually did. I found myself also trying to eat healthy during that dinner and being really annoyed and frustrated picturing her being skinnier and prettier than me. She told me she was going to Vegas for vacation, and I said "good luck keeping up your diet; when I went there it was mostly all-you-can-eat buffets!", and I said it kind of sarcastically. Later, she said she felt like ice cream and I said I had some, but she forgot to get herself some. It took all I had in me to not remind her a million times of the ice cream. I feel so sick to my stomach because it's almost like I wanted to "fatten her up" or something. I remember before her diet, when I started a minor diet, I would always secretly feel satisfied when I saw her eating a bunch of carbs and/or large portions. What is wrong with me??
2. Another example, growing up she was never very good at school and I was. She HATED school and never got very good grades. Everyone in my family always assumed she might go to tech school or just go straight into the workforce after high school. She did, for awhile. I went to college and got my degree in psychology, and now am working on my master's in school counseling. She recently announced that she is going to get her BA in teaching and that she really wants to work in a school. She said she would be very interested in going for school counseling, but does not think she would like to go on for her masters (which is required in my state) so she will settle with being a teacher. This, for some reason, has made me so upset. At first, when she told me, I tried to convince her not to, but then I realized that just the idea of her also going to school and being in the field I currently with I was in (but I'm not, since I did not get my regular teaching license). After that, I told her she should do what she wants but sometimes I'm not as enthusiastic about her hopes and dreams as I should be because I wish she wouldn't be doing it. Deep down inside, I secretly feel like I'm smarter than her based on my experiences with her growing up, and I guess I felt really accomplished compared to her after going through school. I felt like I differentiated myself by going into the field of education and I felt extremely threatened when she said she wanted to do the same. Even the idea of her going to college in general kind of upset me, like made me feel threatened. I'm worried the reason I didn't like it was because before I liked feeling "better" than her, and now we're more on an equal plane, at least career wise. No matter how hard I try to convince myself that it's fine, I still catch myself unconsciously thinking things like "What I'm going to do requires more intelligence, since I hope to work with older kids and she wants to teach kindergarten", or "I will still have a MA when she has a BA" and then I feel like smacking myself because it's so conceited and immature of me to try to reassure myself that I'm better than her in order to make the discomfort go away.

There are many more examples but this post would be too long. It's also worth saying that we also have lots of really, really good interactions. Also, she feels no competition/jealousy of me, it's just me feeling this way with her. I feel really bad but these feelings keep coming.
What is wrong with me and what is some advice to help stop this internal sibling rivalry I've been feeling??

You do not control these feelings. They are like an unwanted guest who suddenly shows up at your house and you cannot readily get rid of.

Accept that you cannot get rid of them.

Each time they come, acknowledge them to yourself, along the lines of a calm "Oh, here you are again,", without judging yourself.

After you acknowledge their presence, go on about your day as you normally would, without judging yourself.

These feelings are not under your direct, immediate control and so you do not deserve any blame for them.

Excellent advice Bill.

Thanks, Bill. That is good advice. I will try it.