all pet owners cry like babies when their beloved friend dies.

You can't have all the rest, the fun and love, and laughing and not cry somewhere along the way! We all have these feelings.

Sounds like the dog is revenge eating. That is what I call it.
Food is #1 to animals. When they see another animal appear, they get worried that they will no longer get enough food. It is only natural. We give each of our cats a treat each day...it is a treat the others don't eat. This keeps the friction down for us alot.
3 female cats in a house can be hissy.

Dogs are notorious for eating cat food. This is because cat food is actually high in fat and protein...so the dogs are drawn to it.
Dog food has lower ratios and more carbs.

We use both wet food and dry. The dry is Eukanuba..which is the higher end of IAMS. I prefer IAMs products because they were the first with EFA technology in them over a decade ago.
Our oldest cat got acne and itching from cheaper dry kibble which was high in corn. Some cats cannot tolerate corn.
The nutritional level of Eukanuba is very good, and our cats are never ill or sick and look very nice and shiney.

If you think she is a kitten still, the kitten version of Eukanuba is excellent. And if she stays outside alot, you'll have to make a house for her. Some people use a styrofoam cooler upside down with a door, and mat inside. She can keep some water and kibble outside, away from rain, etc. If she is really feral she may never come in, or do so only partially. If she were a pet, and abandoned, she will come inside more comfortably.
My son's Tima, loves it indoors...but she tries to run out sometimes but at least she doesn't cry or howl to go out. (he keeps them all inside). We had a friend who adopted a cat not knowing it was mostly very feral. It tore out the bottom of the foundation mattress and lived inside that!

Cupcake is a really cute name. I like it!
Our youngest cat is Oreo-- she was named by the little girls who played with all kittens in her litter. So we kept that when I adopted here, it was cute.