What are distinct facial features that can be considered while drawing an Indian and Caucasian teenage girl?
Here are images of the averages of faces of Caucasian and Indian women.
They are based on images of individuals of an older age than what you're looking for, but should still give a good idea of the major lineaments of women at younger ages:




On the left is an average of young Caucasian women made using this online tool.
In the middle are the two pre-averaged 'portraits' of both Indian and South-Indian women.*
On the far right is an average based on the middle two made in Photoshop.


Impressions:


The shape of the face of Caucasian women is more elongated.
All facial features of Indian women are larger in relation to the size of their faces.
The mouths of Indian women are more plump: their lower lips especially are more pronounced, and the corners of their mouths lie deeper (and/or their cheeks are rounder).


As a side note, I'd like to suggest that in conjunction with (or instead of) this rather theoretical approach, you might want to draw live portraits of individuals. This way, you'll learn to see the individual characteristics, and keep your observations (and artistic interpretation) from being pre-informed.




* source
- These photographs are part of research conducted by Drs. Lisa DeBruine and Ben Jones at the Face Research Lab at the University of Glasgow Institute of Neuroscience and Psychology.
- Rather than downsizing all images, I've enlarged the three images on the right to be of a size similar to the left most image. This might misleadingly emphasize a sharpness of the features of the Caucasian average.