1 The sovereign weed betwixt two marbles plain

sovereign > supremely efficacious marbles plain > [smooth slabs of marble]

2 She pounded small, and did in pieces bruise,

bruise > crush, grind down

3 And then, atween her lily hands twain,

atween > between lily hands > (Cf. Liagore at 304.41:1, who is also versed in "leaches craft") twain > two

4 Into his wound the juice thereof did scruze,

scruze > squeeze

5 And round about, as she could well it use,

as she could well it use > [as well as she could]