I've had big trouble with Mama cat. She was the rescue about 2 years ago. At first everything was going fine then it went downhill.

the problem was she wanted to be an alpha but we already had a well established hierarchy of 10 cats. If mama tried to start anything including our lowest cat on the totem pole, the alpha cat Brendon 10yo Main coon mix and the #2 cat Morgan 6yo rag doll would attack mama.

At first we figure on letting the cats sort it out themselves but it wasn't working.

One thing we didn't do is to take a towel and rub against all of our cats then onto mama to transfer the pack smell on her and reverse. I know this works for chicken. It's a crazy idea but it might reduce the tension.

Sometimes, you have to let the cats sort out their hierarchy themselves. And this means to let them fight it out. You have to be there to make sure no one gets seriously injured. It's nerve wracking to let them "have at it" but sometimes this is what it takes for them to sort out the order in the pack.

I think Izzy is being threatened by Matilda or Izzy doesn't want to become the Omega in three cat household and neither does Matilda.

Since Matilda is the newest, she should be on the bottom of the totem pole. You might want to feed your other two in plain sight of Matilda then feed Matilda last to let her know that she is on the bottom. This may also help.