A perfect setting within Golarion would be Ustalav (I rep that place frequently, great memories, traumatic perhaps, but great). Lot of undead influences, and generally gothic settings. You don't have to go all the way to Geb to find undead underfoot.
A tool I recommend is:
https://www.d20pfsrd.com/bestiary/tools/advanced-monster-search/
Step 1 Toggle Bestiaries and Adventure Path Filter (I like canon products)
Step 2 Filter Type as "Undead" (towards the middle)
Step 3 Generate Results filtered Alphabetically and by CR.
Peruse the monsters at the CR you believe would be memorable for y'all. There might be the perfect entry in there for a BBEG, lieutenants, mooks you could adapt to challenge your hubby and you. Do you want easy things to kill, or do you want the encounter to be heavy, even brawls.
A cult of Urgathoa lead by a lich is something I have been playing around with for a little while. Some members could be necromancers, vampires or any other intelligent undead.
Another idea I have been developing is a priest of Urgathoa masquerading as a cleric of Pharasma in a village that is strangely being over run with undead.
I like the idea of having the person asking for help be a villain as well. She could be a lich in disguise as you say, but that seems a bit much for a CR 10. Maybe she's a vampire or a succubus that needs help destroying the undead lord. A Succubus can easily Bluff/Disguise her way into getting the support of the locals and the player to believe whatever story she wants. She could be 2 or 3 people (male OR female, elf, human, dwarf, whatever) that the player encounters in or around town, all of them supporting a certain story that is being told. Her Succubus powers don't work on undead so she needs others to get rid of them.
That's also a way to work some demons into the mix. The big bad undead guy could have been getting ready for a big fight with some evil power he knew was heading his way, and used his hordes of undead on the player coming after him instead. Then the demon buddies of the Succubus show up once the undead are gone or badly weakened. Maybe that's how the story ends, on a cliffhanger...
The CR9 8th level Sorcerer Vampire qualifies for the Agent of the Grave Prestige Class. If it takes all five levels, it will be CR14. Hit Dice goes from 8 to 13. Casting as a 12th level Sorcerer. Could be a fun BBEG.
If you give the above Vampire one more level of Sorcerer, you can make it the False Priest archetype, and really play with the story options that can come from it.
Using the Agent of the Grave Death's Shroud ability and all the Vampire's charm to hide in plain sight, posing as the priest. His "divine focus" being a bible/tome, the symbol on the front is a decoy, simply cut into the cover, exposing the back of a golden disk that has the markings of the Vampire's true deity, bonus points if this book is covered with human skin. This book contains the divine scrolls that the False Priest can use without destroying, giving the Vampire the appearance of having divine magic.
CR15 (14HD) False Priest Sorcerer-9/
Agent of the Grave-5 Vampire
As a Vampire, it can have up to 28HD worth of Vampire Spawn. Some of which should probably be Negative Energy channeling Clerics.
And with Agent of the Grave/ Animate Dead you can have ~76HD worth of other Undead minions.
This is probably enough to keep one person busy for a while. But shouldn't be too impossible with a character dedicated to fighting the Undead.
The Vampire can actually use the Undead minions to draw attention/scare the people... only faith will save you [insert evil laugh].
For a moment I thought that he'd be the undead with the task of terrorizing pesky intruders. ;)