This paper explores metacognition to Andrews & Sayers' (2015) number sense framework in descriptions of systematic counting competence, using Kilpatrick et al.'s (2001) components of mathematical competence as guides. A case study design was provided to explore a mathematically competent 6-year-old girl's counting and counting strategies when entering the first grade. She is referred to as Agnes. Qualitative investigations of video recordings of a systematic counting interview and a digital number sense assessment were done. Agnes met some of Andrews & Sayers' (2015) systematic counting criteria. Regarding Kilpatrick et al.'s (2001) competence framework, Agnes demonstrated fluency and flexibility in counting, and outstandingly showed adaptive reasoning and productive disposition. Including aspects of Kilpatrick et al.'s (2001) mathematical competence framework seemed to supply appropriate additional information about counting strategies.