You should be talking to her, not to us. We
don't even know what you pay for electricity.
$250/month? More? Less? Where I live $50/month
for what you describe seems very high. My last bill
was $47. (Though we don't leave things on when
we're not using them; we don't have AC or
microwave; we have gas for heat and stove.)
$15 sounds about right to me. If I had to guess I'd say
you were gouging them. But I'm not in your condo
association and don't know the details. What if $15
is not enough and it should be $20? Who cares?
$5/month. You're thinking of paying a lawyer to take
it to court over that? It sounds to me like you and
the neighbor need better communication.