If you're doing three naps the first to go is the evening cat nap. The morning nap usually goes sometime around 1 year or later, leaving just one early afternoon nap.
If you add up the hours of sleep she's getting, it seems like plenty, and if she's happy on such short naps, personally, I wouldn't sweat the situation too much, but I'm pretty go with the flow. Others may see it differently.
Bethany