I would still check with my pharmacist. I have found that your friendly pharmacist is better informed about medication. The fact that it is a capsule is a coating and I do know that niacinamide is a stomach irritant. But to answer your question....
There are flavored drinks that are not juice based. Sweet taste buds are the last to go so you probably want something sweet to cover whatever taste the niacinamide might have. There are also flavor additives that you can add to water in a variety of flavors. The niacinamide and the powdered flavors with water over ice might work. Dad was a sucker for ice cream and that was a good cover even for pills. He like ice cream with chunks and that was just another chunk. Yogurt is a standard for mixing with medication. Sprinkle it on a quarter of a sandwich that she enjoys. Mix it in a little peanut butter with jelly added. You could do the same with egg salad, chicken salad, potato salad, any cold food item. Put it in her Ensure or other food supplement if she is drinking those. If it is safe to crush... you can put it in any cold food or drink that goes in her mouth. Yes, changing where it appears is a good idea.