So would those be suitable for a woman to use, then? And would it still be possible to use them to kill an opponent, presuming they were unarmed or only lightly armed? (I'm interested because I gave my own character a chitin short bow, being vaguely aware of the things you said about longbows.)
Helena, there's a quote from my first firearms instructor that I'd like to share with you:
"Even if you don't have a big gun, you can still kill by shooting straight".
Now regarding opponents - BTW I presume you meant 'unARMOURED or lightly ARMOURED' instead of 'lightly armed' - you can kill an opponent, if you are a good shot. But with weak bows, being a good shot means three things in addition to being an excellent archer.
( 1 ) You have excellent, high quality broadhead arrows
( 2 ) Your target is close.... and
( 3 ) Your target is unaware of your presence!
You will need broadhead arrows, and you can use them with weak bows since the target is 'soft' - that is to say, he is unarmoured. Since your target is close, you will be able to aim for vulnerable spots, and plunge your broadhead deep into them. Since your target is unaware, you will be able to shoot at an unmaneuvering target.
From the back, the best place - but not the easiest place - to aim for is the junction between the head and the neck. A good shot will get an instant kill or spinal cord snap, which is as good as an instant, one-arrow kill.
From the side and front - but I do not reccomend attempting a front shot at close range - the best shot would be, again, a neck shot from the side, and a heart shot from the front.
If you are not sure of your shot, but he is still unaware of your prescence, an excellent idea is to fire one shot through the thigh, and then when he is crippled finish him off with three or five more shots.
This is ninja-style shooting, and so you must remember that the first shot is crucial.