That is a really tricky one. Do you know if the place where you work has a policy about heavy perfume? I worked for the NHS and we were not allowed to wear perfume at all in case it upset patients. You can find out by asking your HR Department and then if they say perfume is not allowed you can tell your colleague "in case she gets into trouble". Failing that perhaps you could explain it to her honestly or, if it makes you more comfortable, tell your manager so that she/he understands why you are away from work so often. Good luck!