First, peonies. These beautiful flowers are currently in season and last about a week indoors once they're cut.
Second, a flower that gives a similar look is the ranunculus. They have crepe paper-like blooms and can last a week or longer in a vase.
Finally, alstroemeria are a great option. They come in a variety of colors and will give Mom two weeks of fresh blooms. Keep in mind, they do drink a lot of water so replenish the vase often.