Yup. What Kristi ^^^ said. I realize you posted because had a question about Sissy's waning appetite, and you weren't asking for dog food recommendations, but you brought up feeding her Beneful. Which is chock full of corn and fillers and lacks much of any nutritional value.
Here's the thing about a dog's appetite....any dog, not just Sissy. Unless a dog is actually ill, they are NOT going to starve themselves. They WILL eat when they're hungry enough even if it's food that's not their favorite, or not what they're used to. If Sissy is fed treats or any amount of table food, she's in all likelihood going to come to prefer that to her regular food, no matter what it is because it tastes better. They're called "treats" for a reason lol! They taste yummy! And most people food is going to have a lot more taste than any brand of dog food, wet or dry.
You first of all need to put your dog on better food. dogfoodanalysis.com has reviews and in depth analyses of the major brands of dog foods. Just as a point of reference, what you're feeding Sissy is in the 1 Star category.
What a lot of us here feed our dogs is in the 6 star premium category...the highest rating you can get, and the healthiest for your dog.
After she's eating a better quality food, you need to put her on a feeding schedule if she's not already. Don't free feed her. 2X a day is enough. You don't mention her weights, but just as another point of reference, my dogs get 1/4 cup TOTAL food each day....that's 1/8 of a cup in the a.m. and 1/8 cup in the p.m. They weigh 3.5 lbs and 4 lbs respectively. Jazz is the four pounder, so she gets a slightly more heaped serving of kibble whereas Tango gets a level one...but still around 1/8 cup per meal, give or take several pieces of kibble
They are HUNGRY when it's time to eat and because they are, they eat all their food at each serving. I'm not starving them, I'm simply not over-feeding them, just giving them the correct amount to keep them their ideal weights.
Typically if a dog becomes picky about their food, it's because they're just not hungry enough, so they're eating for taste, and NOT appetite.