Am at my wits end!

Hi! I am new here and wanted to ask if anyone has gone through this.
Sorry if it ends up kind of long!
I have a 3 year old female calico who is spayed. About 8 months ago she started to really attack her tail.Hissing and growling at it. She had a hard time eating and just walking around because she would spot her tail and go into a complete frenzy.It was so bad that no one including her could get any sleep. I took her to the vet and the determined that her anal glands were infected,they expressed them and gave her a shot and said she would be fine,they told me all the symptoms so I could watch in case it happened again. She was fine for about a week then started again,we took her back and then they said she might be under stress as we had to put down our dog before her isssues came about,that made sense since they were pretty close.He gave me some herbal drops to calm her down,needless to say it didn't help,I took her back twice more and there is nothing physically wrong with her.I started to play with her ALOT and I also started mildly reprimanding her when she started(all I did was show her the water bottle)
In about 2 weeks she was back to normal and stayed that way until this morning.I woke up to her hissing and growling again and running around very frantically.We got a new cat 6 months ago and they do not get along,or should I say SHE does not like the new kitty but is learning to tolerate her. I thought they had gotten into a fight so I got up to seperate them but the kitten was in another room sleeping soundly so I thought "not again"!
I did notice a dry piece of poop on the floor after she got done runnning around. Could she be constipated? Like I said she got a clean bill of health and she doesn't have any signs of her anal glands bothering her. Just now she went to go to a different part of the couch and her tail distracted her and she attacked it again! Is there anything I can do?
Just want mention that when this first started I started thing that she might have feline hyperestsia(sp?) but her only problem is her tail. Also she does not have fleas nor does the new cat. We do get alot of spiders in the house,could it be a spider bite?

Ok you said you got the new kitten 6 months ago, has the cat with the tail issues been to the vet since then? If not, it could be the anal glands again after that amount of time. I know it is gross, but the vet can show you how to express them so you don't need to bring her in every time this happens. My one cat needs her anal glands expressed and last time I took her, the vet showed me how to do it. Thank god I haven't had to do it yet, but if it ever comes up, I know how.

Thanks for answering. The thing I don't understand is after I took her back to the vet the 3 other times when she was acting this way,her glands were fine and they didn't think that was the problem. I am wondering if it is some sort of delayed stress to the new cat,since the little one bothers her quite a bit.When we had to put our dog down she didn't show any signs of anything till about 3 months later.She is holding her tail quite close to her body.

I figured out the problem. Hubby attempted to pick her up and she went crazy. He saw a small hard piece of poop hanging from a long piece of hair from her behind!
She ran off hissing and I wasn't able to get it off of her,but DH just looked and said it looked to be gone.She feels a little constipated,so I have given her a little mineral oil,she has done well on that before. I will watch her closely.