The central argument of the poem is that Avisa is poor, that she is Chaste , and cannot be compared to unchaste Penelope.
In other words she is the opposite of Penelope.
What we need to realise that the writer is using Ironia, everytime he is writing about Chaste Avisa who is poor he is implying the very opposite i.e. UNCHASTE PENELOPE RICH . Avisa is the public face of Penelope Rich she appears to be a virtuous woman but on close observation is actually a hypocrite . Penelope is her hidden unchaste and REAL personality.