yorkie hair grows indefinitely like our hair. It grows about 1/2 inch per month.
Do you know what she weighed at 12 weeks. If so double that for an estimate of adult weight. They pretty much stop growing skeleton wise at about 6 months but may continue to put on some bulk for a few more months. At 6 months my girl weighed about 5 1/4 lbs but now at 18 months she is closer to 6 lbs. If yours is 5 1/2 lbs at 4 1/2 months I would imagine you will have about a 7 pounder when your done (just a guess...could be way off
)