I have enough trouble thinking of gifts I want at my age (43), that I can sympathize with asking people not to send things, especially if she's particular about scents, colors, and/or fabrics. In my case, chocolate is always good, but she may have dietary restrictions or similar.

I would read that as a request for more letters, either gossip if there is some, or just chatty "hi, we're doing well here, I really like my tricycle and Richard and I rode to thus-and-such last Saturday" stuff.

That said, I'm assuming that you have reason to believe this is indirect communication, because the first part, at least, seems fairly direct to me. With "a card or letter is enough" being to make clear that she isn't saying "don't darken my door," just "don't clutter my shelves."