Plan to apply for extension of TRV for mom

My mom has been visiting us on a 6month TRV. Her current visa expires in a month. This is her second time visiting Canada. First time was in 2008.
Now I am hoping to apply to extend her visitor visa for another 6months.

I have a 13month old baby and my mom has been helping me out with the baby as i am working full time. So I am going to put this info in as the reason for her extension.

Could someone pls advise if this would be a satisfactory reason to grant an extension? .. also after an extension within Canada and returning without over-staying ..I have heard several people have been denied visas when then want to re-visit Canada.
Is this true.. ?
If this is the case I want to re-consider applying for an extension as I don't want for her not be able to visit us again..