The elders with dementia often have difficulties in daily activities because of declining cognitive ability. It has been recognized that context-aware reminding systems can assist those suffering from dementia. Reminding systems usually pre-define activities into a plan and prompt the elders if they fail to execute it. However, in real life, people sometimes ignore the plan and choose to do other urgent disruptive activities, that overlap with pre-planned ones. In this paper, we focus on the problem of how to handle the conflicts between pre-planned and real-time disruptive activities. We adopt a planning approach to describe the temporal constraints of daily activities, and define three disruptive activities in our reminding system. A context-aware reminding strategy is proposed, which handles the conflicts between pre-planned and disruptive activities. A simple software tool for caregivers is also presented in order to facilitate their interaction with the system