Tenant moved out and left belongings

Possession - Section 8 and Section 21

Hi

We have a tenant who we have had to evict as she has not paid rent for a number of months. She has been put into a mental health hospital sadly but has agreed to move out on the date issued on the section 21. Her mum and herself have both told us she doesn’t want her stuff so we need to skip it all. The house is very messy and dirty so I’m guessing a fair bit of stuff can be thrown out however morally it feels wrong to throw her sentimental possessions away. She has had her 4 children taken away from her, some of the items belong to them. Legally how long after the date she has left are we allowed to clear out her stuff? And do we need to get permission to remove her childrens items now she is not the guardian of them?