Hi Clare and welcome to BW
first there are 2 books: Secrets of the Baby Whisperer is the original book and goes into the philosophy and techniques etc and the latest book is The Baby Whisperer solves all your problems and is a troubleshooting book that acts like you are having a consultation with Tracy (ie baby only sleeps 45 min, so you see what ideas Tracy would have offered you if you called her to ask, etc)
the main gist of Baby whispering is that you get to know your baby - temperament and cues and use lots of observation to understand what she is trying to tell you she needs. EASY is keeping the order of events consistent (Eat, then Activity, then Sleep) and feeds spaced apart (rather than on-demand or snacking every 1-2 hrs) so that it is clear for example that if baby has taken a full feed at 8am and gets unsettled at 8:45am it is more likely to be tiredness and not hunger because you know she has just eaten...
EASY is a routine but not a schedule - you respect what your baby needs too, so a BF baby at 6 weeks might want to have some feeds every 2.5 hrs rather than 3 and you would feed when she gives hungry cues. if your baby gets tired before the guide in the books you would follow that cue and get her down for a nap (temperament and size can affect how often babies eat or sleep so if they are not "average" or textbook, you adapt EASY/BW to fit them
If she is still asleep at the 3 or 4 hourly mark, do I wake her and feed?
Should I stick to a strict 3 hourly schedule to start?
so for your 6 week old bottle fed baby you could start by trying to get onto a 3 hr EASY and know that if she is sleeping through the next 3hr feed you can let her go as long as 4 hrs between the feeds. just keep track of her total intake of food for the day and it will give you an idea of whether you should alter that - if you notice she goes 4 hrs sometimes, but takes more at those feeds than that is great because her total should be similar to what you are aiming for. if she goes 4 hrly often and does not take more she might be low in milk for the day and will look for more in the evening, etc - tweak and adapt it as you go. Tracy recommends limiting any daytime nap to 2hrs (i would say no more than 2 1/2hrs) to ensure you get enough feeds in and to distinguish between day and night sleeps.
What do I do if she falls asleep while feeding and refuses to wake up?
if this is a regular thing you might stop halfway through the bottle and sit her up to burp her. if that fails change her nappy. usually sitting them up on your knee forces them to wake up though and is enough to get them to keep going with the feed. when you get the book Tracy addresses how she recommends keeping them awake. after the feed simply do the burp/nappy change/swaddle etc. to ensure she is at least slightly awake before you settle her in her bed
If she wake after 45 mins and 3 hours isn't complete do I feed her and start the next 3 hours from the start of that feed?
if she wakes after 45 min and it is not due to hunger than i would spend time using shh/pat to try to get her back to sleep. this is where the sleep training part of BW comes in - this is covered extensively in the books and all over the sleep boards and sleep interview outlines the techniques you can use to extend naps. try to feed only when she is hungry - i know a lot of people think EASY means to feed whenever they wake up and start the cycle again, but it also assumes they have done a nap longer than 45 min. if resettling/extending is not possible then have a little quiet time until she is hungry.
the BW books are more readily available in Australia now - not sure where you are living. If in Sydney they have it at Borders and some Dymocks and Angus & Robertson bookstores and even many of the independent bookstores. i think you can order online through Borders but am not sure. If your local bookstore does not have it ask if they will order it in as many do that these days