I agree with TF/Plano, you need to address the issues of body image and using the bathroom. I suggest those issues are a large part of why she wants to go home. She will still have those issues in first grade.
I think the decision to either keep her in camp or not is not important. There are acceptable reasons for either one. What is important is finding a way for her to be comfortable with her body. Using a swim shirt and shorts might help short term.
How heavy is she? I've now seen 4 children go through Kindergarten. Size was never an issue as far as I could see. How one looks is just not important to five year olds. Kids don't pay much attention until later.
Perhaps you and your wife talk about her size and how she needs to lose weight? Has she seen a doctor? If so what did he recommend? If not, a vist to a doctor is important. Many kids are chunky when they start school. They need the extra fat for energy to grow taller. Small rolls can be expected with some children. Some thin down. Some don't. It depends on their body type.
My grandson was chunky with extra fat until he reached 12. Now he is 5-6 and thin. He's still growing. He was not teased at school, enough to matter to him. His Dad deals with his own weight issues and teased him when my grandson was with him. His pediatrician said that he was healthy and would likely slim down at puberty. He did.
I urge you to talk with her doctor to know if she needs to lose weight. If she does, get a referral to a pediatric nutritionist.
Compliment your daughter. Tell her she's beautiful just the way she is. When she.talks about her body reassure her that her body is healthy. Put way more emphasis on healthy than size.
If the doctor says she needs to lose weight, you and her mother deal with the diet and exercise without talking to her about it.
My daughter was chunky/plump and was gaining weight and gradually getting more round as she grew. When she was 12 or so, her pediatrician, who had been her doctor since she was 7, said it's time to pay attention to diet so that as she grew she would thin out. My daughter never was thin. Her body type was such that she is healthy with a bit of extra fat. She will always have to pay attention to her weight.
I learned to not talk about being fat. When they brought it up, I responded in a positive and noncritical way. "Yes, you are a bit chunky now. That's OK. you will get thinner as you grow. In her teens, my daughter learned about nutrition and exercise so that she felt more in control.
How much exercise does your daughter get each week? Does she spend time outdoors, playing with her friends in an active way. Does she ride a bike or swim, play kid's soccer. Find fun ways for her to exercise. Walking is my thing so we did a lot of walking to the swimming pool, to the store or just around the neighbor to look at trees and plants. We went to the school playground nearly every week.
Do you and her mother feel good about your bodies? Our kids take on our attitudes.