Three metaphors in "Full Moon and Little Frieda" are as follows:
"A spider's web, tense for the dew's touch" which is technically personification, but personification is a form of metaphor, a form of imagery.
"A dark river of blood, many boulders..." is a metaphor for how the water looks in the dark: a metaphor.
"The moon has stepped back" is personification (which is a form of metaphor), and the rest of the quote ("The moon has stepped back like an artist gazing amazed at a work / That points at him amazed") is a simile.
"A pail lifted, still and brimming - mirror / To tempt a first star..." is a metaphor, comparing the surface of the brimming pail to that of a mirror.
Every poem speaks specifically, and uniquely, to each reader. I cannot speak for how the poem "speaks" to you. However, it is the imagery that the author uses that describes with lovely details the scene of this particular night when Frieda notices, with joy, the moon above her.
The imagery also is "painted" in such a way that it seems to reflect the sense of that simile noted above: "The moon has stepped back like an artist gazing amazed at a work." The moon is compared to an artist who stares amazed at the beauty it has created with its reflected light, while that beauty, with equal amazement, points back at the moon. (This reminds me always of the picture "Drawing Hands" by M.C. Escher (1948).)
The very art that is so carefully described in the moonlit landscape is created by an "artist" that a part of that landscape (Frieda) is equally amazed by. As with the "chicken or the egg," debate, where does the admiration begin? With the moon looking below (metaphor) or the child gazing upward?
This is, of course—as I mentioned before—based upon my perceptions of the poem. I hope this helps.