"She is not an actress, but she is a model."
Translation:Ella no es actriz, pero es modelo.
look good, even better than duolingos translation. You could omit 'Ella' as you say 'actriz' and 'es' we all understand you are talking about 'ella'. And you could also omit the 'una' before both professions,
I understand your confusion, we don't have a thumb rule for professions, you have to get to them. 'modela' is not used.
just one thing pero: to express a concept different or give more information on the thing exposed sino: to express somethjing negative againt something positive If it is not clear let me know. In this case sino is better than pero
i think it is perfect, maybe, 'ella no es una actriz sino un modelo', but as you used 'una' in spanish for this sentence you can omit the subject.