This is a fascinating book, if only for pointing out that there were (good) English Renaissance women poets.
Mary Sidney has sometimes been credited as being the real Shakespeare, in that she wrote all his plays and poems, and the Stratford man was merely her "front". She wasn't. Any (even cursory) readings of her poems will show that she is completely different, in style, in content, in form, (in quality?) from Shakespeare.
Okay, we only have Sidney's religious poetry, whereas Shakespeare wrote nothing that is unambiguously about religion at all, but Sidney's Psalms show an utterly different approach to poesy: a wide variety of different styles, line-lengths, rhyme-patterns etc where Shakey used either pentameter (usually) or tetrameter (occasionally) and either couplets or quatrains for rhymes, unless he was showing something special. Sidney is writing Psalms that can be sung, and (like a large number of church hymns) the words are sometimes deeply profound, sometimes close to doggerel to fit the rhyme and rhythm. Fifth century Hebrew verse, or third century Latin translations of the same, do not necessarily make a good fit for sixteenth century English in Italianate verse forms. There are, as I said, some magnificent pieces of verse in there (that might rival some of Shakespeare's poetry) but also some decidedly more dodgy stuff.
The other thing that we expect (and get) from Shakespeare is ambiguity: Sidney has a clear religious message that she wants the Psalms to present. If the message isn't clear enough in the original, she provides it. From a twenty-first century (post-romantic) perspective, this weakens the poetry: from the perspective of a 1600 Puritan, it probably makes these poems brilliant.
Aemilia Lanyer has the link to Shakespeare in that she may be (but probably isn't) the Dark Lady of the sonnets. She was the "mistress" of Shakespeare's patron, Lord Hunsdon (though whether you can really describe a teenager as the mistress of a man in his late 50s is a moot point), and she has one book of poems, presented as one united work, but really not. The main piece is Salve Deus Rex Judaeorum, a 1610s feminist retelling of the Bible, focusing on Eve, Jesus' mother, Judith, Esther, the Queen of Sheba, etc. I don't know if the bits cut by Danielle Clarke (about 300 lines all in all) are significantly weaker than the rest, but what remains of the poem is splendid: not moving, in the way Shakespeare's, Jonson's, Donne's best stuff is, but forceful, polemical, and all written in a strong ottava rima.
Bookending the main poem are her dedications to notable women of her time, some of whom it is implied she knew really well, some of whom I suspect she merely needed money off. Notable in that they are all addressed to women (and well annotated by Clarke) and fascinating for intimate details, but not that fabulous as poetry. And finishing with her "Description of Cooke-Ham", where she paints a vision of an earthly paradise in Berkshire. This seems to have no clear connection to the main poem, and may have been included because she had written it. It's lovely, but not in the same class as Salve Deus.
Isabella Whitney is totally different: about twenty years earlier than Sidney, and almost all written in old-fashioned "fourteeners", which gives the poems a dum-di-dum feel, like light verse, but strangely, of the three, she's the most moving. Within some poems giving advice to sisters, and letters to friends, one gets the impression of a woman who's been exploited in love, and is really suffering. Yes, the one explicit poem about this could be a modern Heroide, but the feeling seems to linger in the other poems.
As a result, of the three, Whitney seems to be the most "truthful" (and therefore probably the most "feminist") of the three poets. One should be careful about reading autobiography into poems (poets are most notorious liars), but she signs most of her poems in a way that suggests they are "her" in a way that Lanyer's and Sidney's are not.
Time for a critical reappraisal?