I live 3 hours drive away and she never goes out of her house except to go to Dr's appointments. She walks around her house but otherwise can hardly walk. Carers attend just to get her up in the mornings. She moans there is nothing to get up for but is uncivil on the phone, which I find unpleasant. She thinks the world of my brother, and moved to be near him.
Just learn to roll with the punches. Ask her which horse is her favorite, say you'll talk to her later. Her "curtness" is more likely a reflection that she feels pushed and challenged to refocus when she's not able to than a direct hostility toward you. You just happened to call at horse picking time.
From this point on everyting is about her. The sooner you realize it the smoother things will go.. She's old, confused and needs your support.. Hugs
And your Mom is right, at 91 there isn't much left to get up for.... imagine not being able to hop into the car to run errands... imagine all of your friends, siblings, cousins had passed on due to age, etc.... imagine every muscle aches when you get up in the morning.... and food doesn't taste good any more because your taste buds are gone. Getting old isn't fun.
If Mom is focused on her horse race, let her enjoy it. You can easily call back later.