I'm losing patience waiting for my girlfriend to reach a more healthy weight.
Why are you losing patience with your girlfriend?
I don't like it when she's not looking at her best.
It's okay that you want your partner to be at a healthy weight and in shape, but it shouldn't be your sole focus. Rather than get frustrated at your partner, try doing activities together for exercise. Your partner is much more likely to participate when it is both of you working out rather than just her.
I want her to be healthy but I don't want to do the same. There are plenty of other things.
Getting into shape is not easy and often people need motivation to keep going. Instead of being impatient with your girlfriend, practice being empathetic and motivational.