Rachel:

It is unlikely that you can “build muscle” ie: Increase muscle mass in your upper body and this would actually very likely be counter productive as it would increase the weight you have to lift to the bar. So, I would not waste time with high reps to failure at this stage. Your issue is that your brain has not yet figured out how to engage the muscle mass you have in the correct way. More on that in a minute.

While there is a great range among women, most women don’t have much of the androgenic hormones that promote muscle growth like men do. They respond to them the same way as men as witness in women body builders who take supplemental hormones to add mass.

Note the bits I wrote in TftNA about women and strength. That’s why I like to use the Max Strength protocol especially for women. If you saw gains then a plateau in your pull up progression using the plan in the book then it’s quite likely that it was working as designed.

BUT>>>>>>

However, if you can not mange one unassisted pull up then I suggest the method cinkirk mentions.
What are called “negatives” in strength training lexicon are “eccentric contractions” The muscles are tensioned to maximal levels as they extend. Concentric contractions are when the muscle gets shorter under maximal load. Much higher forces are possible in eccentric contractions than in concentric ones.

For a warm up do 3-5 sets of 6 concentric (normal pull ups) reps working down to 2 reps as you decrease band assist each set. Then use a stool or somehow climb up to get your chin above the bar. Hold the high position for 1 sec and then slowly lower (no slower than the count of 5). Drop from the bar and rest at least 1 min. During this time doing some other light activity is fine but nothing hard. The repeat the chin over bar/slow lower routine. Do as many of these single repetitions as you can up to 10.

If you can do more than 10 of these single reps or if you can count more than 5 on the way down you need to add some resistance. Even 2-5 lbs will be enough as you gain strength. Do this 2x/week for 4 weeks and see if you don’t manage a pull (or chin) up at the end.

Scott