Instead of trying to measure her,measure one of her tops,pants,dress whatever and compare those measurements with the pattern.That's a lot easier than measuring a squirmy kid.

Also get on the mailing list at your fabric stores they usually have patterns on sale.Most of the time they are 1/2 off at all places,but joann's and hancock run them quite often for .99cents or 1.99 for a couple days.
Actually this coming thursday,the 13 thru the 15 Joann's will have simplicity for 1.99.They also always have a 40% coupon on the flyer and you can also find that coupon at www.joann.com.
HTH
Kathi

When my daughter was this age, I used the Kwik Sew for Toddlers book and patterns, which has been updated for today's styles. (My toddler is 22 now, so styles *have* changed.)

For a little more than the price of one full-price pattern, you have all the patterns you need to make an entire wardrobe. The patterns come on sturdy white papter, each pattern in a different color. You'll have to trace the patterns, but I never found that to be a problem. Made it easier to alter them for my toddler. The book gives very clear instructions about how to sew the garments and how to customize the basic patterns with different trims, collars, openings, etc..

Hancock's Fabric usually has these in stock.

CMC

Here is a link that might be useful: Kwik Sew for Toddlers book