is losing your fingernails a side affect of chemo?

It can be, with some chemotherapy combinations.

I had FEC, and the only effect it had on my fingernails was a white band across them for each chemo; but I remember some women on the breast cancer forums I used at the time saying they had lost fingernails on some different chemo regimes.

As Tarkarri says, she should speak to her oncologist. For other women's experiences, you could ask this question on the forums on http://www.breastcancer.org/ or http://www.breastcancercare.org.uk/

This may depend on the particular drug combination she is receiving.

It should be reported to her oncologist if she has not been warned to expect this.

My own chemo caused a total hair loss but for some reason my nails were stronger and better than ever.

It unfortunately is a side effect of some chemotherapy combinations but i'm surprised her chemotherapy doctor didn't warn her of the side effect!