Mortgage interest ?

The term mortgage interest is the interest charged on a loan used to purchase a piece of property. The amount of interest owed is calculated as a percentage of the total amount of the mortgage issued by the lender. Mortgage interest compounds and may be either fixed or variable.

That is not true.  There are no dependents on a mortgage.  The only reason she would need that is if you were actually going to be a coborrower on the mortgage.

No one needs your social security number for any reason whatsoever if you are not applying for a mortgage or refinancing. DO NOT give it to your mother or any institution unless YOU initiate the contact for something. Having your SSN has NOTHING WHATSOEVER to do with a 'lower interest rate."

Your mother might be trying to refinance with a sketchy company. 

If you're not a party to the mortgage, the bank doesn't need anything whatsoever; it's not your debt, you're not responsible for it, and you would make no difference to the interest.

There's no way she can get a lower interest through you or your ssn and she's BSing you.  Dependants are not put on the mortgage.  Perhaps, you are confusing that with her tax return.  The mortgage rate she will be given is based on the current rate, her credit, and whether she qualifies for any perk, such as being a veteran.  You and your ssn are not going to make any difference whatsoever to her interest rate.  Just make sure you don't sign anything.  You don't want to get sucked into her evil ways, which could have devastating consequences to you, and this is very possible considering what she is wanting from you and telling you. 

If she uses your ss number you are going to be responsible for paying the mortgage off.  

Stop posting this stupid question. 

Nothing about that makes sense at all.

First of all - she should already have your ssn.   (it would be on her tax forms for any year in the past that she claimed you as a dependent.)

Next - there is nothing about you living with her that would lower her interest rates.

It sounds like she is trying to refinance to lower her interest rates and wants to add you as a co-signer.  

She would very likely toss some forms at you soon after and try to convince you to "just sign this" for some reason and you would actually be signing to be on her loan.

DO NOT DO ANY OF THIS.  

she might qualify for a better interest rate with you on the loan....

she's scamming you, she is trying to put you on the loan and that will make you legally responsible to pay it....but i find it odd a parent wouldn't keep a record of their kids SSN

Your mother wants to add you as a co-borrower.  You need that like a hole in the head.  It would make you jointly and severally responsible for her mortgage until it is paid off meaning you would be stuck with this for the next 30 years. 

If she does not pay, they can collect the mortgage payments from you. 

Will it lower your credit score?  It certainly will because it would be listed as your debt.  At best it means you cannot buy a house of your own.  At worst if Mum does not keep up the payments, your credit will be utterly destroyed.  Do not go near this.