To be honest, it would be weirder if she WASN'T mentally ill. It's not uncommon for children to develop a personality disorder after having been dragged from one foster home to the next during childhood. I don't know about you guys, but if I was stuck in her body and making my living as a circus monkey, I'd also be quite depressed.
The thing is that I personally don't sympathize with those that constantly use mental illness as an excuse, have all the means to get themselves help, but just choose not to because whining is more convenient. Or even worse, the ones that are not willing to put in the work, go to therapy once and then proclaim that it doesn't help. No shit it doesn't. There are plenty of people who cannot afford therapy and meds. Amber is not one of them. She doesn't work, lives with someone who can drive and doesn't work, and never stops bragging about how much money she makes. The fact that she doesn't know that antidepressants aren't skittles and you can't stop taking them on a whim really shows that she doesn't give a fuck. It's the same with her weight. She could easily pay for (legit) nutritionists and weight loss surgeons, but for some reason prefers being morbidly obese. I really don't understand why you wouldn't want to solve your problems if the solution is right there.