Perfectly normal for autos to show starting week 3 and on. How much she stretches will be the answer. Ive had autos go from 8" to 50" during the stretch and I've also had autos go from 10" to just 21" with the stretch. If you feel she's a bit small, you can either start over or if you have space, you may be even able to drop another seed since you do not have to worry about 12/12 light change.