My advice would be to apply for a dependant visa (settlement form VAF2) as I think it is unlikely you would get a visit visa as they may guess that your mother would not wish to return to Pakistan (we had a visit visa refused for this reason) and you cannot apply within UK for settlement unless you have more than a 6 month visa (visit visa is 6 months only).
Go to this website:
www.ukvisas.gov.uk
then to SITE MAP and look up the details for:
Family members (INF 6)
This will give you all the information that you need (see below). As your mother is under 65, it will be slightly harder to get the visa. You will have to prove, with evidence, that no-one in Pakistan is able to care for her.
Can parents, grandparents and other dependent relatives go to live in the UK?
If you are a widowed parent or grandparent aged 65 or over, or parents or grandparents travelling together and one of you is 65 or over, you may qualify if:
* you are completely or mainly financially dependent on children or grandchildren living and settled in the UK
* you have no other close relatives in your own country to help you
* your children or grandchildren can support you without needing help from public funds, and
* your children or grandchildren have enough accommodation, which they alone own or live in, where you can live without needing any help from public funds.
If you are a parent or grandparent under the age of 65, you may qualify if:
* you are living in the most exceptional compassionate circumstances
* you are completely or mainly financially dependent on children or grandchildren living and settled in the UK
* you have no other close relatives in your own country to help you
* your children or grandchildren can support you without needing help from public funds, and
* your children or grandchildren have enough accommodation, which they alone own or live in, where you can live without needing any help from public funds.
If you are over 18 and have a parent settled in the UK, or if you are a sister, brother, aunt, uncle or any other relative of a person settled in the UK, you may qualify if you meet the conditions listed in the previous paragraph and you are living alone in the most exceptional compassionate circumstances.