Law surrounding adults with disabilities

LannieDuck

Whilst there may well be cause for concern, I think you need to be a little cautious about wading into this. It sounds as if you have other reasons to think ill of her mother, and that your sister's view of events is exactly what you expect to hear.

Her mother has been dealing with the day-in-day-out needs of your sister for decades. Is it possible that she displays more challenging behaviour than she's admitting to? She's said that she's left the house before - was her mother aware of this, or did she simply disappear one day? Is she able to interact with her environment in a safe manner, or is she a danger to herself (e.g. overly trusting of strangers)?

I think helping your sister get a social worker will be the best way forward.