I was thinking about this - as you do.
If you talk about a male person to someone else you'd often say: he's a nice guy / chap
but if you talk about a female person what do you say?
She's a nice lady (quite "formal" and opposite to What a nice gentleman?)
She's a nice girl (not really suitable for someone over a certain age - and again opposite would be what a nice boy?)
Is there a generic feminine version of guy / chap?