Yes, this is a very common and expected reaction. The oral rotavirus vaccine can cause mild, temporary changes in bowel habits, including loose, greenish-yellow, or sticky stools, as her body builds immunity. Since she is exclusively breastfed, the best step is to continue frequent nursing to keep her well-hydrated. This usually resolves on its own within a few days and is not a cause for concern. However, please consult your pediatrician if she develops a high fever, signs of dehydration (like fewer wet diapers or dry mouth), blood in her stool, or if the loose stools persist beyond a few days.