if she indeed does meet the criteria, a more reasonable adult amongst your family could take the role of temporary guardianship; though this would require deliberation in court and support documents by medical professionals.

I would highly advise speaking to a mental health professional about the legalities and possible ways to mitigate the situation.

Also, is your mom consistent with her medication? I'd imagine quetiapine/risperidone/paliperidone or one of their variations somewhere in the prescriptions - these have to be taken consistently as prescribed to manage the moods/symptoms (her behaviour of watching the mentioned news and buying stuff sound like behaviours of acting out); the problem with those meds is that they need to be consistently taken at least for 1-2 weeks for it to start to take effect as they need to saturate in the bloodstream - also they are not the answer, but they do help to blunt the symptoms at least while therapy/guidance simultaneously can help with reducing life stressors or making negative life choices that comes full circle to increase stress. If she is not taking medication, especially with schizo-affective disorder, you need to take action - the condition is not a death sentence, but when not managed really affects the lifespan of the individual and their caregivers (syrsly stress kills).

If your mom is still on followup with a psychiatirst, then i would recommend that you accompany her for said followup and then request for a social worker whom you can speak to - about how her behaviour is affecting the household.

The next option is to give a call to Singapore Association for Mental Health or (SAMH)Brahm Centre and speak to a mental health professional about managing the impact of your mom's behaviour on the household and options available for that. I will not recommend family service centres in this case as they are woefully inept wrt mental health - our fsc are largely (90% of fscs) only good for paper pushing and providing financial assistance, I will recommend going to or calling Singapore Association of Mental Health SAMH or Bhrams centre to make an enquiry - they will either be able to help you directly or assist in pointing you in the right direction. You can also drop a call to Comunity Health Assessment Team (CHAT) - they are affiliated with IMH and very well aware of mental health related issues.