As Obie has advised, your mother doesn't qualify for an EEA permit as you are now a British citizen.
If your mother is intending to apply for an Adult Dependent visa, you should be aware that this route to settlement has been virtually closed since July 2012 when the Rules were tightened.
In order to qualify, your mother would have to show that she is unable to carry out simple tasks such as bathing, dressing, preparing food etc and that care is either not available in her home country or is unaffordable.
There have only been a few successful applications since the 2012 rule change and the majority of these have been after a lengthy and costly court appeal, or have been submitted in countries where the cost of health care is higher than the UK, such as the USA.
You should also bear in mind that if you apply for an ADV and it is refused, you will be closing the door to your mother visiting in the future due to the previous intention to settle in the UK.
These articles by Freemovement explains the situation clearly.
https://www.freemovement.org.uk/out-with-the-old/
https://www.freemovement.org.uk/home-of ... ndparents/