That's a really good question. From what I understand it partially depends on her current strength, riding style (climber vs. TT specialist), typical cadence and her ideal strength, riding style and cadence. Honestly there are probably more tech experts in the Tri forum- so post there if you haven't done so already, but from the bits of stuff I've heard, I'd put her on a 165 or 167.5, based on her height alone. But I'm far from being a bike fitter or techie.

Some other questions: what bike is she on? 650s or 700s? Does toe overlap freak her out or no big deal?

I'm 5'4'' and recently changed from 165mm cranks to 155mm cranks. It made sense if you looked at my inseam length of 29". Leonard Zinn uses a guideline (loosely) of 21% of inseam length for crank length. I now know what it feels like to actually "spin". Before I was working hard all the time. It literally took me minutes to adjust to the shorter cranks. I'll never go back! Other factors should also be considered. An experienced fitter should be able to help. My bike is also 650c size.

Jacqueline

Thanks im gonna look for 160's