According to this calculator, a 5'2" 400 lb woman could expect to end up around 226 lbs on average, leaving her still obese. That's the 50th percentile result at 18 months, when patients generally stop losing weight.
A 80th percentile result is 249lbs and a 20th percentile result is 203 lbs. Both are still obese on a 5'2" woman, of course, and none of this accounts for the weight regain WLS patients usually experience. There are people who end up normal weight after WLS, but it's very rare and it's due to the patient's own dedication to healthy lifestyle.
If Chantal gets the bypass surgery through some medical negligence of the surgeon, and somehow doesn't kill herself by bursting her stomach, and somehow miraculously follows the post-surgery diet...she'll still be a fatty fatty boombalatty.