The white tablets probably don't contain food dye, but you need to read the label to be sure. Look at the "inactive ingredients" list.
But, she should be aware that the calcium carbonate in Tums isn't always the most absorbable form of calcium. Calcium citrate tablets are a better choice, if you can afford the price difference. If not, she should take the Tums with food in order to maximize the absorption of the calcium.