How and why do the rhymes at the ends of the lines reflect the critical though playful tone of the young woman who is speaking?
"The Nymph's Reply" is not a love poem; it is a rebuttal of Marlowe's "Passionate Shepherd to His Love." Whereas the shepherd is idealistic in his seduction of the nymph, she is realistic in seeing through the poetry. He will make her "beds of rosies," but she knows that once spring is gone, the roses will be "rotten" and soon "forgotten."
Stanza by stanza, the nymph responds to the shepherd. For every enticement he makes, she gives a practical reason why it can't be. At the end, she says that only if youth were eternal and seasons didn't change, "Then these delights my mind might move/ To live with thee and be thy love."
Read the two poems side by side, and you can't help seeing how they speak to each other.
They work in this poem because of the author's tone. Diction sets the tone in this poem. Despite the use of the words you mention, the fact that there is rhyme adds a playful quality to the poem and lightens the tone of the poem. The shepherd's attempt to woo the nympth was so "heavy" and serious (and hollow, in my opinion) that it is almost comical!