I agree with your identification of the ribbon as the India General Service Medal (1895). The patterning looks right with the equal bands of Red/Green/Red/Green/Red. It is hard to tell the exact colours of the original from the various examples on the internet.
The Queen Alexandra's Military Nursing Service for India was a separate, though parallel, organization to the QAIMNS until the two were combined in the 1920s.
The Indian GSM was replaced in 1909, so it would seem Matron Carter served in India some time between 1895 and 1909.
Maec