I have asthma, and it doesn't affect me. If she's really worried, I'm sure s/he comes into contact with plenty of wood each day. As long as it's not really dusty there shouldn't be a problem. S/he could always use a paper bedding or fleece.
I am allergic to any products that have dust, but as far as I know Aspen is relatively dust free compared to other woods such as pine. She may actually be fine with it. I know that I cannot used kiln-dried pine, so that is why I have switched to fleece.