Exactly this. At the moment, trans girls and cis girls are well-defined and commonly used and accepted.
The use of the term cisgender or the prefix cis- to refer to individuals whose gender identity matches their biological sex is not required but can be helpful in avoiding ambiguity when discussing transgender issues. That said, we do not have a code of acceptable gender-related expressions and do not wish to referee terminology. Please be considerate of the feelings of others and avoid needless provocation when using gender-related terms. If you feel others are using gender-relating terms or expressions improperly and you wish to correct them, please do so in a civil manner.