The rose is a rose,
And was always a rose.
But the theory now goes
That the apple’s a rose,
And the pear is, and so’s
The plum, I suppose.
The dear only know
What will next prove a rose.
You, of course, are a rose
But were always a rose.

I think the poet is pulling the beloved’s legs .Firstly ,the rose is a cliche to describe female beauty and if that is what she is looking for ,well ,let her have it. Between the two of us, she is not all that a rose .She may not deserve to be called a rose but what is there in a name and you do not lose anything by calling her a rose. If an apple can be called a rose, why not the beloved? Secondly, what is so big about being a rose? A pear or an apple can as well be the rose. The way metaphors go, you can call anything a rose ,and they are so worn out through centuries ,such tired cliches! Everything has its unique identity that cannot be called something else.Thirdly a rose is so boring, in terms of a fixed identity of standing for beauty, a hackneyed symbol for fragile beauty. Of course she is a rose, if that is what she would prefer.