Strokes rarely affect taste sensation in isolation, although it's certainly possible depending on the location of your mother's stroke. What's more likely is that one of the medications she's taking
is affecting her taste. The first thing I would suggest is that you talk to her doctor about whether her medications can be adjusted so she doesn't have this side effect. That would be an easy solution.
If it actually is stroke related, it's a much tougher problem. It's actually a combination of loss of the sense of smell and the sense of taste, and it's very challenging because nothing tastes good. You may have to supplement her nutrition with very high-calorie foods so she doesn't lose too much weight. Very severe cases may require the use of a feeding tube.