My mother in law has two years multiple visa to UK, she has

your mother is in possession of a 2 year long-term Standard Visitor visa. That is the type of visa that she holds.

A visitor can apply for and be issued the following'

1. standard visitor visa. This allows on entry for up to 6 months.
2. 2 year long-term Standard Visitor visa, this allows multiple entries to the UK during that two year period, each visit can be for up to 6 months.
3. 5 year long-term Standard Visitor visa this allows multiple entries to the UK during that five year period, each visit can be for up to 6 months.
4. 10 year long-term Standard Visitor visa this allows multiple entries to the UK during that ten year period, each visit can be for up to 6 months.

So as you can see, each the only allows visit for up to 6 months at a time. The actual visa itself would specify how you the visa lasts before applying for a new visa.

So yes she can after the six months leave the UK, to visit somewhere else and then return to the UK for uptown another 6 months.

What you need to be careful of is how you have worded her say here. You said "I need her not to go to India, but she has to stay with us permanently"

If immigration learn of this, she could be refused entry. The visa is a "visitor visa" not a permanent visa. There must be no intention to us that visa to stay permanently.

It may be possible to consider the visa type "Apply as an adult coming to be cared for by a relative"

As a child of your mother, if she would be coming to the UK permanently to be cared for by you this visa might be good. The link here explains.

https://www.gov.uk/uk-family-visa/adult-dependent-relative

Sorry, I cannot assist with that, I am not acting as your lawyer here. There is no Client / lawyer relationship here, this is an online advice portal only.

I would advice they you arrange to visit a local immigration law form in your local area to discuss the finer details of how to and when to make such an application.

It may be helpful to instruct a local solicitor who specialises in this area of law. You can find a local firm using the Law Society website. www.lawsociety.org.uk

Once on that website, you can click on the find a solicitor option located just above the Law Society logo. Select quick search, then select the area of law required and enter your post code. A list of local firms will then be displayed.

Can I assist or clarify anything further?

Correct, I cannot assist with the application for her to stay here. The is only online advice we do not represent clients here.