Thank you for your question and patience, I’m Tom and I’ll try to help you.
As you are an EEA citizen, then it would be for her to apply for an EEA family permit to come here and join you if she is eligible.
However, as she is your mother in law she would only be regarded as a family member for the purpose of applying for this is she is “dependent” on you, see “Qualifying as a family member” on the following link for confirmation:
Therefore, you would have to show her that she is financially or socially dependent on you.
If she can look after herself and does not depend on you for money then she would probably not be eligible and the application would be rejected.
If she could not look after herself and is dependent on you then you could attempt to apply. However, it’s a complicated application to make and you would have to instruct a UK basd solicitor to take your detailed instructions, draft the application and advise you of the necessary supporting evidence that you need to submit with the application.
If you consider that she is dependent on you then you should book a consultation with a local immigration solicitor with a view to instructing them to act on your mother’s in law’s behalf for the purpose of applying.
My goal is to provide you with a good service. If you feel you have received anything less, please reply back as I am happy to address follow-up issues specifically relating to your question.