Thanks for bringing this fine poem to my attention.
The poem seems to be an extended metaphor (sometimes called a "conceit") about the poet's difficulties in matters of the heart (that is, love) and her friend's seemingly effortless success in such matters.
Flora, the friend, always seems to hold the Queen of Hearts, which symbolizes love, or perhaps what we would call today "emotional maturity." The poet, no matter how much she cuts and shuffles the deck, never seems to draw the Queen of Hearts.
The poet tells us that once she was deceived by the Queen of Clubs, which appeared to be the Queen of Hearts. Perhaps this symbolizes a time that the poet thought she had found love, but was later disappointed.
In the poem's conclusion, the poet wonders what her friend's secret is; is it:
skill, or craft, or luck in you:
Unless, indeed, it be