Hi cousin,

Although it is not common about 5% of MS patients develop psychosis including visual hallucinations.  MS Trust (a nonprofit) has a good article on Abnormal mental states in MS.  Here is an excerpt:

"If a person with MS becomes psychotic (especially if there is acute onset) it is important to rule out physical triggers such as chest and urinary tract infections and metabolic disturbances. Steroids, baclofen and dantrolene have all been reported to trigger psychosis in people with MS so a close review of the treatment history is vital. People with severe depression may develop psychotic symptoms congruent with their mood - for instance delusions of poverty or guilt - and here treatment should be aimed at the depression. Finally, psychotic symptoms in MS may be the presenting feature of dementia.

"People with MS are particularly sensitive to neuroleptic (anti-psychotic) medications. Rigidity and bradykinesia are commonly encountered even at low doses of conventional neuroleptics such as haloperidol. Therefore, atypical antipsychotics Seroquel (quetiapine) or Zyprexa (olanzapine) should be first line therapy in this situation. The few studies about the prognosis of psychosis in MS suggest that treatment response is fair."

Depression is extremely common in people with MS.  It sometimes takes experimentation to find an appropriate anti-depressant or combination of anti-depressants.  As mentioned above, hallucinations can be a side-effect associated with some drugs commonly used in MS.

Sounds like it is time to consult your cousin's neurologist and perhaps have an assessment done.  If this is the result of an infection, then definitely it needs to be taken care of.  If it is the result of medication, again needs to be taken care of. 

If it's a result of the disease itself, then a new treatment approach probably needs to be taken.  And if she is in danger of harming herself, then emergency measures need to be taken.  Please call the doctor or go to the ER if necessary.