It is important to put in detail about how often and for how long direct intervention is required at night eg twice for 10 minutes each time to go to the toilet etc. Tick all the boxes that apply in relation to why the person needs to be watched over at night: to prevent wandering, harm to self and others, lack of awareness of common dangers, confusion and so on. I found it useful to make use of the spaces for additional comments to set out the case in more detail.
Typical wording would be along the lines of (tailor these to give an accurate description of your particular circumstances):
"X requires support, encouragement and help with all aspects of her personal care. This includes using the toilet, cleaning teeth, taking medication, undressing and putting on night attire. Without support all of these will be done incorrectly or neglected."
"X has advanced dementia and cognitive defects. She is disorientated to time, place and person and has poor recall. She needs constant support, supervision and guidance throughout the day and night to maintain her health and welfare."
"X confuses day and night. Without constant supervision she will fail to undress for bed, attend to toilet and hygiene needs or take medication. She gets out of bed at any time of night and will dress as though ready for the day. She often also confuses dreams with reality."