If she is 90 years old, give a lot of consideration to the idea of giving her a new dog as a present.
Dogs are good company but they require a lot of attention, maintenance and money for food and veterinary care.
If she is in need of a walker, a new dog will have to be trained to keep out of her way so she isn't tripped by it.
Will she be able to house train the dog? Will it need a doggy door to gain access to the yard for potty breaks when she's unable to let it outdoors herself?
Will she be able to give it the physical exercise it needs?
As for gift ideas, here are some questions from which you can get some gift ideas:
What are her living conditions? Is she still living at home? Has her home safety been improved with the addition of safety grab bars in the bathroom around the shower, and toilet? Does she have a shower chair and hand-held spray nozzle for use in the shower?
Does she have any extended reach grabbers to help her pick up things from the floor or reach things on high shelves?
Have most of the daily items she uses most been moved to either higher or lower shelves for easier access?
What about a stool for her to sit on while at the bathroom sink doing her routine hygiene and makeup? One might also be helpful to her in the kitchen so she can sit while preparing food.
Are the pathways in her home clear of furniture and obstacles so she can safely maneuver around with the walker?
Does her walker have useful accessories such as a basket or tray to help her carry things while using the walker?
Is she in need of a service such as Life Alert to call for emergency help if she needs it and can't reach a phone?
If she doesn't already have these things, she'd greatly appreciate items that will help her safely through her daily activities. If you are not near her to install these things for her, you can hire a handyman to do it for her.