Please help me stressed cat

I have a 2 year old spayed cat. She is very aggressive and has been since I got her when she was 3 weeks old. Monday I got a new female kitten who is 5 weeks old. My 2 year old doesn't know what to think of her. In the beginning she hissed and swatted at her. Now she just watches her like a hawk to see what she is doing. My problem is that my 2 year old cat has not gone poop since I brought the new kitten into the home. She is eating though. I'm worried she's going to get all backed up. Is this normal. Is she just stressed from the kitten and things will turn out fine? Please help..

i would think if she was stressed she would not eat.....though all cats can react different not poopin could be something medical. I would be inclined to vist the vet

How many litter boxes do you have? Each cat needs a place "to go"! Try using a minimum of three boxes or maybe more depending on the size or layout of your home.

Your cats should not be together right now. Separate them, make sure that they can see each other, but not get to each other. The resident cat will be upset and stressed by the new scent in the house and the disruption of routine.

Make sure that you have two litter boxes for each cat. You can try the following to help your kitty try and pass stool but don't be surprised that she has pooped and you haven't found it (gone out of the box). Usually under the bed or under chairs or in corners are good places to look-

Give the kitty some loose leaf organic catnip to eat
Add some canned pumpkin uncooked to the canned food
Cooked yams mashed with a bit of butter
Add some metamucil to her canned food powder only

I have a nervous cat, when I got her from the shelter she had been overgrooming and had no fur on the insides of her thighs on her hind legs and then she started on the backs of her front legs! My vet recommended a mineral supplement called serene-UM. A feliway plug in and some Bach's herbal remedies have also been recommended.