Based solely on the cover, I thought this was a book about a bear! But, no. Gloria is a bulldog who gets her nose out of joint when her best friend, the youngest child of a group of three siblings, gets a new doll for her birthday.
The older two kids try to engage Gloria and pull her out of her slump. But everything they try (from baths to toys to walks) just makes Gloria grumpier because all she wants to do is play with the little girl. (The little girl is shown playing with her new doll on almost every page, and pretty much ignoring the dog.) It isn't until one of the older children's schemes backfires that Gloria gets exactly what she's been wanting all along.
The text is rhyming and full of rhythm, much like in the author's Llama Llama books. I think this is one of her earliest works, though, since the author bio at the back only made mention of Llama Llama Red Pajama. The books about the llama and his friends are stronger, but Grumpy Gloria isn't terrible. It's kind of amusing, and shows the strong bond between the dog and the little girl.