If it is her own poo then it is the same E-coli as she already has in her intestine, so not introducing any new ones. It is spreading the bacteria aroiund from one person to another which passes on disease.
I'd say it is unpleasant but not to get in a flap about it. It is a common habit of small children. Just make sure she is not left with a full nappy long enough to get at it.
"Normal microbiota
E. coli normally colonizes an infant's gastrointestinal tract within 40 hours of birth, arriving with food or water or with the individuals handling the child. In the bowel, it adheres to the mucus of the large intestine. It is the primary facultative anaerobe of the human gastrointestinal tract. (Facultative anaerobes are organisms that can grow in either the presence or absence of oxygen.) As long as these bacteria do not acquire genetic elements encoding for virulence factors, they remain benign commensals.
Therapeutic use
Nonpathogenic Escherichia coli strain Nissle 1917 also known as Mutaflor and Escherichia coli O83:K24:H31 (known as Colinfant[) are used as a probiotic agents in medicine, mainly for the treatment of various gastroenterological diseases, including inflammatory bowel disease." Wikipedia