simply misus'd: utterly disgraced; she has also misus'd (buggered, fucked up) the prate (backside) of her own sex.

love-prate: lover's chatter

pluckt over your head: stripped off (like a servant unworthy of their uniform)

fathome: a unit of depth (= six feet)

sounded: measured

Bay of Portugal: Here the water is about 1,400 fathoms deep; the Bay of Portugal is also, from other texts as well, a metaphor for great sexual capacity. Rosalind wants Orlando to fathome (clasp or embrace) her and fathome (penetrate) her bay (vagina), but his depth (penis size) is still unknowne to her.

bottomlesse: Rosalind thinks her affection is bottomless, or endless, but Celia thinks it bottomless, without foundation/baseless. Orlando is a bottomelesse vessel so as fast as Rosalind pours affection in, it runs out. Celia also hints that Rosalind's own bottom (vagina) is bottomlesse (insatiable). So much bottom (semen) has been pour in to Rosalind's "Bottomless Pit" (vagina) that it runs out again.

shadow: shady place; Rosalind plans to sigh until such a time as Orlando's shadow (the "cock of a diall", the part of a sundial that casts a shadow) will shadow (sexually cover) her. Then she will come (orgasm) beneath a shadow (canopy for a bed).