Also your mother would have to prove that she is unable to manage basic daily tasks such as bathing, dressing and preparing food AND that help is either not affordable or is unavailable in her home country.
There have been very few successful applications for an Adult Dependant Visa since the Immigration Rules were tightened in July 2012. Most of these were from countries where the cost of care was higher in their home country, such as the USA, or after lengthy and costly Court appeals.
If your mother applies for a ADV and is refused, this will close the door for future visitor visa applications, due to the prior intention to settle in the UK.
(Casa, not CR001)
Please don't send me PMs asking for immigration advice on posts that are on the open forum. If I haven't responded there, it's because I don't have the answer. I'm a moderator, not a legal professional.