Attitudes

In May of 2013, I adopted an 8 year old cat (Sassy).  She is quiet, sweet, and well-behaved.  She NEVER jumps up on the counter or tables, and she doesn't get into trouble.  She likes to sit next to people but does not like to be held.  Almost 3 weeks ago, I adopted a 1 year old cat (Cupcake) that has turned out to be the total opposite of Sassy.  Cupcake is always on the counter, digging into something.  She chews holes in bread bags and even a pizza box the other day.  She antagonizes Sassy and invades Sassy's space.  I anticipated that there would be an adjustment period for the two cats and I didn't get Cupcake so Sassy would have a friend, I got her so that my daughter could have a pet that is more playful and would appreciate all the attention my daughter gives.  Well, now the issue is that Cupcake is trying to be the dominate one and is chasing Sassy away from the litter boxes.  So Sassy has started using our bedroom (pillows, bed, clothes forgotten on the floor) as her personal litter box.  I have the patience to let them get to know eachother and I can deal with the hissing and growling but I can't deal with the litter box issue.

I have separated everything to no avail.  They have separate eating areas, sleeping areas, plenty of space (bi-level house) and I provided three litter boxes for them.  Sassy only uses one but Cupcake will use all of them.

I don't know what else to try except for getting rid of the new cat.

Have you separated THEM?

Here is an article about how to properly introduce cats http://www.thecatsite.com/a/introducing-cats-to-cats

You have only had Cupcake for 3 weeks.  In many cases, 3 weeks won't even be enough time to get through step 1 of the introduction.

Basically, you should isolate Cupcake immediately and start from scratch, moving very very slowly and making sure not to proceed to the next step until BOTH cats are comfortable at each juncture.

Also as an FYI Cupcake is just being a 1 year old cat.  She'll need lots of patience and some training

Good luck.  I am sorry you are going through this.