She makes a reasonable point in the sense that arguing against obesity purely on grounds of health could be reframed into a strawman that you should hate disabled people because they are also unhealthy. Obviously it's the choice involved with obesity that is key, but it is important to remember that hating fat people just because they are fat and ugly is all you really need. Hating them for their health consequences overcomplicates a simple idea sometimes. It opens the door for them to nitpick "what is health and how is it defined?" and "when exactly is someone at fault?" and these questions lead to endless, semantic, subjective arguments with no end. Alternatively, you can tell them they are disgusting and call it a day.