Sorry to hear about your sick grandmother. I'm not a doctor but I've spent some time studying this while caring for my boyfriend who received a chemo regimen. If in doubt, ask the nurses where she's getting therapy.
Probably not a concern under normal circumstances. Remember you are constantly exposed to people receiving chemo when on the bus, train etc. You just don't know it. But it is a good thing to be aware of, since these drugs are toxic. The risks of the drugs are worth it to the patients receiving the drugs, but for those around it is important to minimize exposure.
Studies have found the drugs and their metabolites are found in body fluids of people receiving the drugs, mostly in urine. It is important to avoid contact with urine for the days after the patient received chemo. As a precaution, patients are advised to sit down on the toilet while urinating, and flushing the toilet twice with the lid closed. The toilet should be cleaned with gloves. Gloves must be used when empying a bedpan etc. with urine and care be taken to avoid splashing. Linnens, bedsheets etc. soiled with urine, vomit etc. should be washed as soon as possible (or stored in sealed bags) - glvoes shuold be used when handling these sheets, and they should be washed separately from other stuff, preferably twice.
The above is the usual advice Ive seen to spouses etc. to people receiving chemo. For people caring for patients at oncology wards (who may be seeing a lot of patients receiving chemo every day during their entire work life) some extra precautions are advised:
Certain drugs (incl. cyclophosphamide and thiotepa) can also be found in smaller amounts in sweat, and can be found in clothes, linnes, bedsheets etc. from patients receiving the drugs. It is advisable to change linnes, bedsheets etc. 2-3 days after infusion of drug, preferably using gloves. The same is true for clothes worn during those days.
Remember that the drugs quickly flush out of the system (in most casea a few days), so it is only the days shortly after infusion that special precautions must be taken. Otherwise just use common sense and normal good hygiene :) And don't let this disturb your caring for your grandmother, she needs all the support she can get. Good luck :)