Hi there, I do not have this problem, but I’m a PT and we have actually more people than you would think with this or very similar problem.
I did not read through prior feeds so this may have already been suggested, but see if you can find a pelvic floor specialist (PT) or one that knows how to do nerve glides for this region as it may not be just the pudendal nerve as there are many nerves off the lumbosacral plexus and if the fascia is tight surrounding it (yes-psoas definitely could be clamping down causing symptoms) then those muscles and tissues need to be released.
If she has been sitting funny bc of it she likely has some thoracic and lumbar alignment issues now and may have a ‘functional’ scoliosis developing (functional meaning she wasn’t born with it, but bc of postural dysfunction her muscles have pulled her spine into various curvatures that is correctable with both manual therapy and specific neuromuscular re-education). These postural faults could also be causing or feeding into the problem even if it gives temporary relief sitting like that.
The pelvis and sacroiliac joint need to be assessed and corrected if out of alignment.
So basics that any good manual PT (one that specializes in manual therapy) can do is correct lumbar facet dysfunction followed by pelvic dysfunction, followed by releasing the tissue throughout that whole region as the fascial system overlaps and even her abdominal fascia up to her ribs I bet is tight as well as in her low back, pelvis and down to both knees.
Lastly, I’d work on checking nerves you can glide (sciatic, femoral and obturator) and do some nerve glides, teach how to perform at home and if a pelvic floor PT-prob knows some fancy ones that are more specific to that area.
After all that correction manually, then comes core stabilization of the transverse abdominis, pelvic floor and multifidi-basics first (Sahrmann) and then work on correcting posture (schroth-seated and sidelying).
Sorry for all that, but just wanted to help. Feel free to copy and paste and print all that out if you go to PT they’ll know what to do (if you find a good one). If they just use modalities (Ultrasound, estim, ice/heat, ionto) and exercise alone, you aren’t going to likely fix the problem. IMO. She should feel immediate relief in the first 3-4 visits-if not, may need to shop around. Look for (OCS, COMT, FAAOMPT, etc) for initials after their PT, DPT. Good luck