My mother will be interred shortly, can an inscription be placed on the gravestone?

Sorry for your loss. There is a form that the funeral director gives you. It has the allowed spaces for you to fill in. Basically a short phrase.

Yes

To a certain degree, yes. there is a format for the gravestones, so there is only a small place for an inscription.

Yes, the cemetery should ask you what you would like to put on the gravestone