Risk management
1) The lady with dementia must be asked her views. She may not have capacity to make informed decisions, but before that's established it's got to be assumed that she does, and her views sought.
2) Her capacity needs to be assessed. If she can make valid choices, then whatever she wants to happen should happen.
3) Her risks need to be assessed. If there are risks (of self neglect, or accidental fire setting, or hostility to others, say) then these need to be addressed. Maybe they can be contained/manageable within the community, may be more speciailised care is needed to meet those needs.
4) After assessing her risks and her needs, if she's agreeable to the advice that health care professionals offer, then this care plan can be put in to place. If she's not agreeable, and there're no risks, then she does what she wishes.
5) If there are risks, and these are significant, and she's not got capacity to make informed decisions, then case law shows that health professionals are obliged to act in her best interests (e.g. placing in EMI residential care, if that was what's needed) even if she can't co-operate or consent to this. Clearly, her male carer will have input in to what he feels would suit her best, and may be able to guide on whether a small unit with few people may suit her (as she's always liked a cosy, small, friendly set up) or a huge more anonymous massive care home is better (as she's always been a provate person and like to walk a lot) or whatever.
6) If there are risks, and these are significant, and she's not got capacity to make informed decisions, and is opposed to care plans, then statutory instruments are considered. This could rarely mean the National Assistance Act, but invariably it's the Mental Health Act 1983 that can be used to admit her for assessment and treatment (treatment being broad, not just medical) and then placement. Her next of kin has input (and rights) if this Act is used.
As well as considering situations where she's decreasing capacity, and increasing risk, and increasing opposition to support, were there any other issues you needed to consider?
Edit : oh, as far as work with various professionals goes, yes, it has to happen. A GP will often co-ordinate care. Mental health services will organise hospital care, but also often guide on community care. Social workers will advise on practical and social care. Approved social workers will be needed to consider the balance of the lady's freedom/choices and her needs/risks and decide if the Mental Health Act is used (only approved social workers can make applications to detain people, not medics), and a psychiatrist would need to be involved for a medical recommendation. An occuptaional therapist is often involved in looking at functional level, how to improve or keep this, what help can be put in to place to make things work. A physiotherapist can help with mobility and safety issues. Pharmacists can guide on how to make medication regimens simpler or safer or more effective. Community nurses spend a lot of time supporting carers (including staff in care homes) with advice and ideas. Voluntary organisations including Age Concern or local groups can assist with delivery of advice and direct care (such as respite or sitting or day or holiday care). Any good team will invariably work with a broad ange of folk, to get the best outcomes through using a range of approaches.