Hi- It depends on who is asking. Are you looking to have this rental income from Mom help qualify you on the mortgage needed to buy the place? If so, then probably not. Most lenders will not allow that for a mother/ immediate family member. Unless there is a lot of documentation and she has done that in the past with you,etc.
If its an IRS question, then I would assume you don't want to show it as rental income anyhow. You'd have to ask you CPA that.
I guess it depends on if you are getting a mortgage or not. And what kind of mortgage. If someone is paying you rent for 6+ months a year, it is an investment property not a vacation home. And investment properties are harder and more expensive to finance for you.
If I can be of any help, please let me know. Thanks,