Oh that old hijack.
Re (from Smiles
"I just don't know how to let her know Perlina and I have an open marriage and I want to go out sometime ..."
Personally I think I'd mention/describe the open marriage first ... then let that sink in for a few days/weeks (and make sure Estrella is cool with the idea of an open marriage) before asking Estrella out. Perhaps you could reassure her by giving her Perlina's contact info so she could confirm first-hand that Perlina was okay with it?
Asking someone out is always a risk. Nature of the beast.