Shadow and Owen have never really gotten along like the other cat. They tolerate each other and give each other space.
Shadow is okay with the other cats. I have three. Shadow is 12, Sookie is 12 and my scaredy cat one, and Kudos who is Owen's best friend. They were all here before we got Owen.
Shadow is 12 years old and healthy. Still acting normal and eating, drinking , and using bathroom.
Lately she has become aggressive towards Owen. Even if he only walks by. She has tried to claw him and now Owen is scared to walk by if she is in the doorway. I will say she gets this meow that can set Owen off and then I have to break his concentration. I am thinking this meow means I want to fight.
We are wondering if this is a normal thing for senior cats to go through? Or is this a behavior that can mean something is wrong with her health and needs a vet visit.
As usual any other information needed just ask me please

House cats generally live to be fifteen and older (even into their 20s!). I'd definitely get Shadow checked out. It could be a toothache or who knows. Have you noticed any changes in behavior other than toward Owen? -- litter box problems or eating changes or sleeping places/times are different? Oh, and Shadow has been neutered, right?

Actually Shadow has been spayed.. All my pets are spayed /neutered. Well except for bunny but she has to finish her antibotics before the vet will do it.
No other changes that we notice.
I should mention she (as well as the all the other ones) are on the 2nd month dose of fleas. We had a flea issue, which shocked the vet as they are not supposed to be in Alberta (too cold)
She gets along with the other cats by ignoring them. Shadow was a rescue who was neglected in her other "home". She loves sleeping with Henry but once he goes to work she sleeps on a mat in the kitchen. I move too much for her. She is supposed to be my cat but she chose Henry as the one she is the most attached to.
Thank you WG I hope I gave you enough info

Having lived with cats all my life, I know they react to changes in the household. Nothing different in that way? You haven't moved furniture or changed a schedule for something? Is something different about Henry? Does Owen smell different?

Only thing different is my brother is out of town. He got back late last night. He does not bother with the cats at all. Hard to believe but there are people who are not cat people. GASP!
Also the weather has been odd lately. High winds, thunderstorm warnings etc. The cats are all indoor cats only.

Any disruption in the household can set off bad behavior. Our cats pace and snarl at each other during bad storms, so hmmmm on that one. I'd still rule out something physical like teeth problems. Oh, and the flea treatment could have gotten everyone a bit off too. We went through that a couple of years ago with cats under the bed and fighting with each other (I think from the weird feeling as fleas crawled out of their fur).

Thank you will be making a vet appointment for her.

Thank you will be making a vet appointment for her.
Be sure to report back and post what happened. Sweet Owen doesn't need an ornery cat in his life.