The basic answer to this question is no. A stroke causes brain damage, but that damage should be limited to the cells that are affected by the event itself. A
stroke should never grow in size over several years. It sounds like something else is happening.
I would guess that your mother has one of a few things going on. The first possibility is that she is having additional, smaller strokes. In my experience, after looking at brain scans on many patients, a “symptomatic” stroke, such as the one your mother had 5 years ago, is really only the tip of the iceberg for a larger number of smaller “asymptomatic” strokes that happen much more frequently due to small cholesterol plaques and aging of the arteries. These add up over the years to cause an overall decline in brain function. These may have contributed to some of her new symptoms. Another possibility is that she is having an overall decline from a different brain disease altogether, such as dementia. Finally, she may be having general medical problems which are affecting her brain, and making it more difficult for the healthy brain tissue to help out the damaged cells.
I would strongly encourage a check-up with her doctor, or a referral to a neurologist, for additional scanning and some basic blood tests.