Frighten her with all the stories about bloody awful care homes. Shouldn't be hard - they're all true.
Tell her how it will cost £1,000 a week - a week - minimum. And how you don't get anything you ask for, that once they're in, that's it.
How clothing goes missing, and valuable items, and it's regarded as just one of those things by the care home manager.
How they get roused to be washed and changed at 6.30am in the care home every morning anyway, if they can't do it themselves.
The overall lack of control.
Or how long-standing couples get separated by penny-pinching local Councils who always side with the care home against the family.
How once certain residents get past a point, a programme of covert dehydration is applied, without the family's consent or knowledge - won't be long then, and it saves the Council and the NHS CCG money.
And how, should the family suspect and raise concerns about low fluid intake, the care home can go to Adult Safeguarding - the Gestapo of adult social care - and have said family barred from the care home - ensuring the covert pathway programme goes ahead unimpeded.
Explain how the care home GP will be in the pay of the care home, and in no mood to bite the hand that feeds. Sinister euphemisms like 'TLC' - Tender Loving Care - will be liberally sprinkled over your parent's medical notes, implying the end is near. Afterwards, you won't be able to prove a damn thing.
Especially how you won't even be allowed to look at your parent's medical notes if they didn't know to grant you Lasting Power of Attorney in Health and Welfare while they were still able to. Terms like 'severe dementia' can be sprinkled all over them, whether true or not - if it's written down, it becomes true, so the thinking goes. Everyone can see those medical notes, other than you. (Incidentally, I suggest you get LPA in Health and Welfare while you still can)
And how most care homes are at the rough end of some very nasty outsourcing - they are only in it for the money, and nothing else.
CF: living in their own home, and knowing they have to get up at a certain time.