THIS IS KIND OF A SPOILER but my guess is Betty actually does have cancer. Here’s my evidence:
1) She meets her friend in the cancer ward. Her friend says she sometimes wishes she had never told anyone that she had cancer — that she had just kept quiet and then faked a car crash.
2) After calling Don in a panic, she doesn’t actually call to tell him the scare is passed.
3) When she gets the “news” that she’s okay, she exhibits no changes at all. No growth. No kindness. Barely even any relief. At the end of the show, she goes for Sally’s ice cream rather than trying to lose the weight. Perhaps Betty just can’t grow. But perhaps she actually doesn’t have anything to feel thankful about.
4) FINALLY, we know — or at least are pretty sure — a main character dies this season. Also, Betty is kind of an awful character at this point, and I’d be surprised if the show’s creators didn’t know it.