。
She goes by the name Yocchan.
Literal
[topic-は] Yocchan [called-という] name [object-を] is-using.
~という is the workhorse 'X called Y' pattern — here ヨッチャンという名 ('the name [called] Yocchan') uses という as a quoting/naming connector. ヨッチャン is itself an affectionate diminutive: -ちゃん is the affectionate suffix used with names (often shortened to a more cuddly form), and the small ッ before チャン marks emphatic gemination, common in nicknames. So Yocchan would typically be derived from a name starting with Yo- (e.g. Yoshiko, Yoko, Yoshito).