Great goal! This is one of mine as well. I've read a lot on this, and it really comes down to two things for women:

1. Decrease body fat. The less you have to pull up the better (...duh, right).

2. Increase muscle strength. This is usually done by doing hi sets x low reps at challenging loads (i.e. "LEAST amount of assistance required"). For example 5 sets x 5 reps or whatever you can manage. I'm at 3 x Failure (I usually fail about 2 or 3 during my slow decent). But, the key to building strength is to SLOWLY descending your body out of each pull-up/chin-up...like to an 10 or 15 second count. This is the eccentric phase of the muscle contraction, so focusing on SLOWLY lowering your body really taxes the muscle and spurs growth. Depending upon your recovery speed, do this type of chin-up session once or twice a week, but with at least 2 days REST in between sessions. For me, I find less is more, so I do this session once a week.

As you succeed in holding your descents for longer periods of time (hence building more strength), you can take more assisted weight away to the point you are doing a chin-up unassisted.

Beyond that, basically do a little more each chin-up workout session! Whether it's another chin-up rep, or an even slower decent, or decrease the machine assistance, or just add another Set for x reps. Just log what you do and challenge your body, each and every workout session with a little more to promote growth.

Good luck!

Yeah go for it I can help you.
If you do what beastette has said that will work.

But what I did was 5 x 5.

So 5 p/u's then rest
and try it 5 times

Thrn have a day off and do it again the day after that.

it becomes reallt easy and then keep it to 5 sets - but do 6 reps in each,

then 7 reps and so on.

But at some point test yourself to see how many you can do in one big go - on a non training day.

Wehn you can do 12+ i'm sure lots of guy's will be looking at you thinking i wish I could do that.

Well done!!!