Has she or anyone else had access to the house since your father died? For example, did she have a key to the house? If so, have you changed the locks and how long after the death did you do so?
Could she have already taken her things and this is a try on?
In other words, do you trust her?
You are probably not obliged to let her in, but if you don't she will presumably go on raising this issue so it may be best to let her in. But if you do make sure you and at least one other independent person are present with her all the time she is there. If she brings someone else with her make sure neither of them is left alone at any time while in the house. (In other words, don't trust her!)
Of course, she could still raise the issue after she has been in, by claiming that you or someone else has removed her possessions.