It is likely that this would aggravate her condition, albeit, temporarily so it is a matter only you can decide upon. You can, however, mitigate the effects by using a paint with very low or zero VOC content and ensuring thorough ventilation for several days after the work is complete.
I have a friend with a similar condition who has put off doing the same for some time. It has got to the stage now where his bedroom really needs doing and I have suggested he go away for a couple of days while the work is completed.