Becky and Amber are bad for each other. Becky is not 100% to blame for Amber's ballooning weight (Destiny is more responsible than anybody, but let's not go there). However, Becky is absolutely complicit in this arrangement - manifested in her own weight gain. She chose to enter this cycle of enabling and laziness, and she is also capable of removing herself from it. If Amber makes life hard for her when she doesn't enable her, she can choose to tell Amber to fuck off, or to talk it out, or any number of things. Instead she chooses to comply with Hamber's demands. If the relationship is abusive and she has chosen to stay in it, she's complicit. Melodrama about hurt feelings and guilt does not absolve her of responsibility for her actions, nor does it alter the cold fact that Becky could have prevented much of this weight gain.
Amber would be eating like a pig with any girlfriend who would have her, because after Destiny Amber has given up on life. But someone who cared about her, as Becky purports to, would stand up to her and do something about it. Becky has simply complied with every demand because she is either too cowardly to dissent or too selfish and lazy to dismantle her own gravy train, and in either case she chooses the status quo of Amber dying in the near future over risking the material rewards for giving Amber what she wants.
If Becky loves Amber, she evidently does not love her enough to tolerate any kind of material or emotional hardship in aid of helping her. Someone who loved Amber would say "no" and weather the storm. She did not force Amber to gain weight, nor did she offer the slightest protestation to enabling it. Becky is in this for money and for junk-food emotional validation; she can feel wanted and important if she brings Cleopatra her asp, and chooses not to consider what will happen when it bites her. If she is guilty of nothing else, she is guilty of selfishly placing her own feelings before Amber's health and mortality.
