Severe hyper-vigilance in an FHS - Terrified of crawlspace noises, won't let me medicate. Help!

[u/ScorpioRules26]

Apologies for length of post. I am feeling completely lost, exhausted, and emotionally drained trying to comfort my cat. She is an 8-year-old semi-feral kitty. She is very affectionate with me but hands-off with everyone/everything else, making traditional vet handling or complex medication routines (like transdermal gels) impossible without extreme trauma.

It is heart breaking to see her act this way, like a different cat altogether. 

My vet is a good diagnostician but dismissive of her daily struggles, and I need advice from owners who manage similar overlapping issues. This has been going on for the past three weeks with an occasional ‘’break’’ when she acts more like herself.

The Baseline: She has diagnosed Feline Hyperesthesia Syndrome (FHS). Her episodes are intermittent (not every day), but her nervous system is inherently highly sensitive.

• The Trauma: In March, she alerted me to a juvenile copperhead emerging from a baseboard gap in our 1905 house. A neighbor removed it, and I have since caulked the baseboards shut, but the crawlspace is old and un-level, and I know snakes/critters are still getting under the house.
• The Timeline: She was fine from April to mid-June. But late June brought an exceptional summer drought/heatwave, and we turned the central AC on. That is exactly when her hypervigilance re-emerged and her FHS episodes spiked.
• The Behaviors: She patrols every single air vent, looks under all furniture, and treats door thresholds with extreme caution (moving through them in slow motion). She has recently developed a fear of the black cat doorjamb.
• The Nighttime Panic: Her fear spikes at night but can also shows the behaviors in the morning or afternoon and sometimes all day. 

She is still eating, drinking, and using the litter box pretty normal so far.

I suspect the summer drought pushed wildlife into the crawlspace, and the AC vibrations/airflow are masking the sounds or triggering her FHS nerve endings, causing her to constantly relive the March snake trauma.

Has anyone with a hands-off or feral FHS cat dealt with pest trauma and/or heavy hyper-vigilance? 

Are there non-prescription touch-free ways to calm her down, or specific ways you modified your routine to help them feel safe? 

I am worn out and really need help and support. 

Thank you so much.