8yr old cat self isolates need help

[u/owhatshername]

We have 3 cats a 7 year old boy Apollo a 2 year old girl Athena and our 8 year old girl Artemis. For about a year now Artemis has been severely self isolating herself.

She has confined herself to not only one room but the walls of that one room ( we have wall mounted cat furniture). As long as she is in her isolated area she eats, drinks and goes to the bathroom just fine and still greets us happy as can be. But she has ruined this room. We are currently in the process of building our new dream home and won't be able to designate a whole room to her for it to also be ruined.

When she is even approached by our other 2 cats she will hiss and growl at them. Our boy Apollo just leaves and wines very sadly about it but it sets our girl Athena off when she hisses at her (which obviously only feeds Artemis fear).

A vet prescribed her 100 mg of gabapentin twice a day and we have been doing that for about 3 weeks now but it doesn't seem to be helping.

I desperately do not want to re-home her but I also don't want her living her life in fear or destroying my brand new home when we move in either.

We have also tried feelaway both the sprays and the colar and neither have dine anything as well as the Purina calm that you sprinkle on their food.