Hi Mama,
I think that you should do what works for You and Her as a family. There was an article by Katheryn Dettwyler about the average age of weaning in the world and the range was something like 2.5 years to 7 years.
A Natural Age of Weaning Like I said, you need to know what is right for you two. I am so thankful for my nursing relationship with my 4 year old, it has weathered us through some of the most gross childhood flu's etc...
good luck mama,
Misty