Permanent residence for disabled EEA relative

[Baltic Sea]

Hi everyone,
I'm planning to apply for permanent residence. I'm from one of the EU countries.Has been working here for over 10 years , married British sitizen , my child born here. I think I quite likely to be granted the residence. The person who I'm worrying about is my mother. She moved here 5 years ago . At that point she was on similar to ESA benefits in her home country and when she moved first she was receiving them for first couple of years. Then she was told she need to have assessment again but as she livin in UK, she has to apply for it here. Only then she did apply for ESA here and been giving it after proving her habitual residence( on the base that she has all her closest family here: me, my husband and my son). She has been in ESA support group for last 3 years.
What is her chances to be granted permanent residence if she will apply now?
Has anyone had similar situation and applied for permanent residence?
What is the best, apply separately or together?
Thanks a lot.