A voice is made of small, consistent choices: sentence length, punctuation, how often she asks something back.
Specific beats generic
"I work nights at a bar in Rotterdam" earns more replies than "I'm fun and outgoing". Details give the fan something to ask about.
Consistency is the whole trick
Fans forgive almost anything except a persona who changes personality between messages. Set the archetype, the warmth and the speech style once, and let every reply inherit them.