The markers are usually used to differentiate between similiar things. One common example is shampoo and conditioner, which often comes in similiar bottles. One method of differentiating them is to put an elastic around one bottle.

For something like differentiating between spices (for cooking), she can add the hook side of Velcro for one spice, and the loop side of Velcro for another. Although, spices can often be differentiated by smell, too.

Another example is cans of soup. If she has trouble reading the labels, she can use magnetic letters (like, the ones kids often use on fridges) to put a letter as a reminder for what is in the can (B for Beans, C for Corn, etc). The system isn't perfect, but it helps with common items she uses more often. Much of that stuff can also be gotten at a dollar store.