An important part of the narrative structure of The Faerie Queene is the prominence of characters that find themselves doubled, mirrored, or copied. Weird, we know, but also kind of interesting. Of course, on the largest level, pairing is also something that guides the structure of the text, since almost every knight is paired with a lady, some paired with a guide, and we encounter many sibling groups etc.
But, it's worth thinking a little more closely about moments of very explicit copying, such as the creation of the false Una by Archimago in Book 1 and the creation of the false Florimell by the witch in Book 3. The false Florimell in particular becomes a pretty major character, attaching herself to various knights and completely confusing everyone. So, what's the deal with this double trouble?
Spenser is very interested in the power of appearances and images, and is particularly concerned about how we are able to make judgment calls based on what we see. The doubles of these women (who are always themselves very innocent and chaste) are extremely forward and flirtatious. They act out this problem of how we make judgment calls and force characters who come across them to make a decision. Spenser doesn't seem particularly optimistic about our ability to identity the real thing since both the false Una and the false Florimell deceive pretty much everyone.
We can also think about the creation of these doubles as a moment where Spenser is thinking about his own work as poet, a task that in the Renaissance was understood to be guided by a process of imitation—basing your work of art on the work of art of another or something in the natural world. Imitation, for Renaissance artists, was the highest form of flattery.
There was a certain amount of anxiety expressed at the time about this practice of imitation and people worried that it was just a glorified version of deception. Spenser seems to be thinking that through here, and differentiating these false copies from his own art. Both the false Una and the false Florimell are produced out of a malicious desire to deceive, different from Spenser's desire to educate with The Faerie Queene. But it might not be as simple as that—what do you think?