If your mother is really elderly and desperate....and you have this relationship with Jesus and are happy......then why are you even letting it get to you? Give you elderly mother a break. Its coming from a place of love. She isn't the watchtower brand. She is just your mom.
If you want you can call her, thank her for thinking of you, but let her know that you won't read it. I offered my mom a deal once. I'll read whatever you want sincerely and with an open mind, if I can send you some critical literature I already have verified isn't full of misquotes and untruths, and she can do the same.
We already know where that goes. then change the subject. Talk about life, your family....the things her authentic self want to really talk about anyways. I find the conversations always go JW when there is nothing else to talk about!