In Alice in Wonderland, Dinah is Alice's real-life* cat, mentioned in chapters one to four, where Alice is thinking of her, but Dinah does not actually appear in the story. There is no connexion between Dinah and the Cheshire-Cat.

As Alice is falling down the rabbit hole in Chapter 1, she has a lot of time to think, so she begins musing that Dinah will miss her very much tonight, and hopes they'll remember her saucer of milk. She then apostrophizes her cat (addresses her directly though absent), saying she wished she could be here. There are no mice in the air, but there are bats, and they're very like. This then leads into her reverie of 'Do cats eat bats?' and sometimes 'Do bats eats cats?', for as she couldn't answer either question, it didn't matter which way she put it. (A nice Carrollian touch of logic there, I think.) Just as she imagines earnestly asking Dinah about ever eating a bat, she lands with a thump!

In Chapter 2 Alice meets the Mouse, having fanned herself small enough to fall into her own pool of tears. On failing to get a response on addressing him in English, she tries the only French she can think of, Où est ma chatte?, first sentence in her lesson-book. This naturally startles him, and she hastily apologizes for mentioning cats, but assures him that he would become fond of cats if he knew her dear Dinah.

She then expatiates on Dinah's merits, calling her a quiet, dear thing, and 'and she sits purring so nicely by the fire, licking her paws and washing her face -- and she is such a nice soft thing to nurse -- and she's such a capital one for catching mice'. This has entirely the wrong effect on the Mouse, as does her subsequent mention of a neighbour's dog (never named).

Towards the end of Chapter 3 when Alice has once more offended the Mouse and caused him to leave after he has told his long and sad tale, and she and all the other creatures in the Caucus-race (the Lory, Crab and so on) have called on it to come back, Alice makes another unhappy mention of Dinah.

'I wish I had our Dinah here, I know I do!' said Alice aloud, addressing nobody in particular. 'She'd soon fetch it back!'

'And who is Dinah, if I might venture to ask the question?' said the Lory.

Alice replied eagerly, for she was always ready to talk about her pet: 'Dinah's our cat. And she's such a capital one for catching mice, you ca'n't think! And oh, I wish you could see her after the birds! Why, she'll eat a little bird as soon as look at it!'

Since most of her audience are birds -- Lory, Duck, Dodo, Eaglet, Magpie, Canary -- this causes a sensation, and they quickly leave. Alice sadly reflects that no-one down here seems to like Dinah, but she is sure she's the best cat in the world. And she begins to weep for loss of her.

Dinah is mentioned twice more in Chapter 4, first when the White Rabbit has ordered her to fetch another fan and gloves, and she imagines after being sent on messages by a rabbit, Dinah might start giving her orders, such as to watch a mousehole. But she wonders whether the family would allow Dinah indoors if she started behaving like that.

The second time is when Alice has grown large enough to fill up the White Rabbit's house and, being more confident at this size, is resisting attempts by the rabbit and his servants to get her out. The Rabbit says, 'We must burn the house down!', at which Alice calls out, as loud as she could, 'If you do, I'll set Dinah at you!' This causes instant silence among those outside.

* It really was the name of the Liddell family's cat.