if you go by this growth chart (
http://www.yorkiepassion.com/growthchart.htm), it says your puppy will be 5 lbs full grown. you said she was 1 lb 4 oz at 5 weeks old (which is 20 oz), then i'd estimate 5 lbs. she'll be bigger than you want (you said about 4 lbs), but she shouldn't be a monster size. however, the growth chart is just a reference guide. there's no guarantee it's accurate. but who knows.
just thought this might help ease your worries a little. this chart is universal pretty much. if you type in "yorkie growth chart" in google, you might find a different one, but so far i've found the same one on several different sites.
good luck!
