Something else that can be tried at the same time or after a few weeks on the diet is acupuncture. See if there is a certified verterinary acupuncturist in your area.

If you try these things and the kitty is still pulling the hair out, you might try a lesser drug than Prozac. Chlorpheniramine is a mild sedative and anti-histamine, so that would be the first one to try. 

Amitriptylline aka Elavil would be the next notch up. I have a couple of cats on that and it just takes the edge off things for them. Both of those drugs are very inexpensive. 

Then you get into the big guns like Prozac, Buspar and Paxil. Even though she did not do well on Prozac she may be okay on the other two. They all have a different mode of action.

I really believe in trying the natural route first, see if the body can heal itself.

Also make sure that you give her lots of attention - especially when she is not tearing at her fur. You don't want to reinforce that behavior by making a fuss over her when she is doing that.

I hope this will help. I am sure it is very distressful to have a cat that is literally pulling her fur out.

Purrs to you and Missy. Please let me know how she does.

Is Emerald a shy cat? Confining her is the first step in getting a handle on the problem. Can you put her in the bathroom for a while? If this seems drastic to you, it isn't really. Cats tend to feel safer in small spaces, and it would be temporary. If you are reluctant to confine her, increase the number of litter boxes and locations in the house. For three cats you should have three litter boxes and some experts say one more than the number of cats so that would be four. But start with three. You can put 2 side by side and then one in a separate location. Scoop at least once a day, twice is even better.  

Use unscented clumping litter in them. Some cats also prefer to urinate in one box and defecate in another so the side-by-side boxes often work well for that. The box in another location allows Emerald to avoid Penny if she is using the box. I would give her lots of attention at this time. If you decide to confine her, and if she is good for a couple of weeks, start letting her out for supervised excursions to the rest of the house. After a month of good litter box habits you can probably start to let her range through the house unsupervised, but you might want to still confine her to the bathroom while you are at work and maybe at night while sleeping.
Let the cats interact in a positive manner during this period. If they like a feather toy, play with them together. If they like treats give them to them together.
You might want to put a collar and bell on her so you know where she is. 

You did a good thing by rescuing Penny and you got a little more than you bargained for, but it could work out with a little patience and TLC for Esmeralda. Let us know how it goes.

Litter Box Retraining – General Guidelines

Used for inappropriate urination, not spraying. Always have your cat checked by a vet for a urinary tract infection. Some infections are subtle and require antibiotic therapy for up to a month, or perhaps anti-inflammatory drugs and/or a special diet. It is very important that medical causes be considered first and then treated appropriately.

Confine the cat to a crate - a large dog crate or kitty playpen is ideal. Place one or two litter boxes in there with unscented scoopable litter. Set up the boxes so that there is some space between the food and water and the box(es) There should also be room left for a bed or sleeping pad. Leave the radio on a soothing station like classical while you are not there. Put the crate in a room that you can use to expand kitty’s territory when using the litter box consistently, like a bathroom or spare bedroom. The room should be fairly small though. Once kitty is using the boxes consistently you can open the crate and let kitty out in the room. However, even if using them right from the start, keep kitty confined for a week. Take out for short periods of cuddling, grooming  or play, two or three times a day, but then back in the crate. Try to give attention equivalent or greater than what was received before confinement. Fifteen minutes of undivided attention per day can make a big difference. This confinement should not be viewed as punishment. Do not leave kitty unattended outside the crate, even for a minute to answer the phone etc. 

Another option is to put the crate in the room the cat has spent the most time in, and feels more comfortable in. But supervision is crucial.

Don't think this is cruel, it is behavior modification, and environment control, and if surrendered to a shelter, kitty would be in a smaller cage for a week or more during quarantine and acclimation. After at least a week of consistently good habits open the door to the room and let kitty out for supervised periods and give lots of attention, then back in the crate at night and when you are not at home. As time goes by and there are no incidents outside the crate you can expand territory. If there is a slip, go back to the level before the slip i.e. if kitty slips after being let loose in the main house, go back to room confinement. These steps should be gradual and always with close supervision when gaining the next level. Always keep the cage box(es)available during this period and consider adding others on additional levels of the house if warranted. Stop letting kitty outside, if kitty was outdoors in the past. Going outside won't help the problem. You can convert kitty to an indoor cat and this is the time to do it.

Another thing that can be used when confining a cat is Rescue Remedy. You can put it in the water or directly on the cat's tongue. Use it consistently. It is very mild and sometimes the effects are subtle, but they are there. You can get this in a health food store. It is also available from various online sources.

Feliway may be helpful if there is an anxiety component associated with urination outside the box.

All soiled areas must be thoroughly cleaned with an enzyme cleaner such as Nature’s Miracle.

Don’t give up. This behavior is a way of communicating. It is up to us humans to figure out what our kitties are trying to tell us.