She could have put her foot down strongly. What is the use of a pooja when the worshipper is in a bad mood? It is better not to do any festivities/poojas rather than do them with a bad feeling in the mind. Not good for her or them. If she continued the mourning for many years, then it is not good, but for an year, it would have been fine. Unfortunately, some people are like that. They would rather let their authority run than care for the actual outcome.