I used to shorten my bars all the time until I got the '08 and decided to leave them stock length. Shortening the bars won't make the bike more twitchy but it will reduce your leverage so when you drop into something the front wheel will have a little more leverage on you and it's easier to "tuck under"
If you are having a problem with feeling like you are too far forward roll your bars forward a bit. This is one of those counter intuitive things but it does work. Rolling the bars forward causes you to stick your, er, rear back as you drop your body position to compensate. You also gain forward and back leverage because your arms are more in-line with the bars. This will make the bike more twitchy and faster turning. You will definitely notice on the loop but it will also make the bike feel better on drop-offs as it will be easier to get your weight back and low and will help on uphills as you can pull harder on the bars to weight the back wheel.
As for Renthal vs. stock I was always a big fan of Renthals. There are three main dimensions for bars. Height, sweep and rise. Height can be considered the distance from the triple clamp to the mid point of the grip location of the bars. Sweep is the angle the grips are bent back from the plane of the center of the bars. Rise is the angle the grips are bent up from the center of the bars. Much of this is personal preference but at 5'7" you are pretty much within the norm for the standard bars except for the difference in shoulder width/arm length/torso length because you are a woman. That fact alone can affect your perception of the bikes geometry. There is no one answer and the best recommendation is try different settings for bar position to find what works for you. There are also set back pegs and moving the forks up/down in the triple clamps to fine tune steering response. Play with it all. You seem pretty competent with a spanner.
What bars did your friends' bikes have and did they have accessory pegs?