If you outright call her fat, it's going to piss her off. I can guess this because clearly the communication in your relationship is not strong enough for comfortable mutual honesty, otherwise you wouldn't be asking us. So there is some degree of imbalance there and not just her weight. If you want change, you need to focus on changing yourself and hope she follows but without expecting it.
Don't be a dick about this if you don't want to be treated like one. How would you want to be encouraged to lose weight? Especially in terms of how she gained it, from an injury which has caused her not to be able to participate in a major life passion of hers. That sucks.
So I would recommend working on communicating with her (and not all at once) and start changing yourself what you want to see in her. IYSWIM.
Don't be a dick about this if you don't want to be treated like one. How would you want to be encouraged to lose weight? Especially in terms of how she gained it, from an injury which has caused her not to be able to participate in a major life passion of hers. That sucks.
So I would recommend working on communicating with her (and not all at once) and start changing yourself what you want to see in her. IYSWIM.