Adding Calories to Pureed Food

Try adding some extra calorie-dense ingredients to whatever she is eating. Fruit juice can add taste and calories to bland food without being filling. Some protein powder may help. Nuts and seeds are good, and so is avocado. A little olive or canola oil can add calories, as long as she likes the taste. Look into baby food. Some adults find it quite tasty. See if your mother would eat more overall if she had several small meals throughout the day.

Water and Weight Gain

Water itself does not cause weight gain, though you should continue to drink the 8 or more glasses daily that is generally recommended for good health. If you drink a lot of water--more than you need--you will gain weight temporarily, but you will lose it as soon as you sweat or urinate away the excess.