I also love [name]Penelope[/name] (number one for years). I was concerned about popularity earlier on and thinking of alternatives and was considering [name]Paloma[/name] for a little while. Has a similar feel to me and [name]Polly[/name] is a great nickname for it !
What about [name]Parthenope[/name]? It was the name of [name]Florence[/name] Nightingale’s sister, inspired by the city of Naples. Nice mythological associations, too.
In English, [name]Penn[/name]/[name]Penny[/name] was originally short for Pernel, Petronel or Peronell, the feminine form of [name]Peter[/name].
Then there’s the recent celebrity baby called [name]Penna[/name].
Alternatively, you could go with something like Petra Nicole or Perla Niamh.