I know exactly where you’re coming from and it’s a horrible feeling because you feel so guilty for not being able to be truly happy for your friend’s successes in whatever form. When I’ve felt this way about a friend in the past my fear came down to two main things:
– that the friend would notice that they had become ‘better’ than me and would start behaving as if they were ‘better’ than me, which would lead to a rejection of sorts and more emotional pain which would confirm my inferiority.
– that others (this was even worse for me) would notice this superiority and start acting on it.

I knew that if my friend or others were to act as if there were some kind of hierarchy of a person’s worth in terms of their attributes (appearance, cleverness, social behaviour etc) then that would be extremely shallow and something that I did not want in my life, but thought that perhaps that’s just the ‘harsh truth’ and the way life inevitably ‘is’. We cannot help judging others, after all. It is part of being human.

However, it does not have to be like this. Remove yourself from these social-media generated, black-and-white hierarchies and see the bigger picture. You are enough as you are. Jealousy is a horrible burden and will only hurt you, it will never motivate you to become ‘better’, at least not for long. When you can be completely and genuinely happy for your friend’s successes (and everyone else’s) then things will fall into place and you will feel peace. It’s not easy and your feelings are natural; it is a good thing you have recognised the damage they are doing. Facebook and other social media makes these feelings 1000000 X worse but what you see on a screen is so rarely a true depiction of real life. Just as you say that nobody would be able to see the jealousy you carry inside, your friend is likely doing the same thing in some way and has her own set of emotional issues that she is grappling with.

Be honest with yourself and embrace how you feel, jealousy and all. Don’t try to talk yourself out of it or rationalise it or mentally punish yourself for feeling this way. Just accept the feelings and then try to find the place beyond success and failure and winning and losing. Remember you (and her) are enough just as you are and nothing will change that.