| Don't buy! Don't buy! Don't buy!
The sizes are for the size kid you have. Typically, the scroll should reach the middle of the palm when held correctly. It's best to have her measured by a teacher or music store you can trust. 4th graders come in all shapes and sizes, so don't assume what size they need.
Getting a good violin is easy if you rent from a reputable store. Many teachers will tell you to avoid the Chinese instruments, because they feel they are inferior instruments. This is not true at all. Some great instruments come out of China these days, which wasn't the case in the past. Some well known brands that make good violins are Glaesel, Knilling, & Meisel, but keep in mind that brand name isn't much of an issue in the orchestral world like it is in the electric bass world. An instrument is either good or it isn't, regardless of brand.
Most stores will rent you a smaller size violin, and will allow you to trade up to the next size when necessary. Once she's gotten to full size, many stores will allow you to use some or all of the credit towards the purchase of a new one. Make sure you read the rental contract! Don't bother buying a smaller size violin; she'll just grow out of it.
And please, for the love of god, have her learn how to tune and change strings. Violin teachers are notorious for not teaching how to do this: the most basic of upkeep on any stringed instrument. If I had a nickel for every time I had to tune a students violin for them... | 
