I would try 2 shots of Lute... 10 days apart... just to try to "reset" her cycle... might throw everything else into a reset? Cheap to try... cycling regularly does not mean she is "right" inside. Any chance she is a free martin? They can cycle if all the "parts" are not there inside.... If she is having any hormone issues, the Lute might get it back on tract... or try the route with using a cidr....
That would not cure the udder situation except maybe through the hormone "reset"... I would be at my wits end.... and yes, I get the pet, first calf raised and all that.
Honestly, if you had a bull available, I would stick her with a bull and if she is cycling, he will put alot more semen in there and as often as she will stand...
One of my dairy farmers I test for, had a heifer they showed. Could not get her bred AI... cycled regularly. Vet could find nothing wrong. Finally asked if we would run her with an angus bull to just get her bred. Sure, no problem... out with a group of heifers with the bull....comes up Open... everyone else in that group pregnant... okay, moved her to another pasture... saw the bull breed her... back in heat and across the fence she goes to the neighbors bull... got her back and we switched out our bull for another when ours came up with a foot problem...
When we brought that group home we thought for sure she had settled... took her back to the dairy farmer and he was having a regular monthly herd check that next week... NOPE... still open, still everything felt normal... vet said ovaries felt fine...
They shipped her.... and she had gotten a bit of an udder so that is why we were sure she had settled...
She didn't have any udder problems but would not settle. Had AI and 4 different bulls... with months to breed. Some just don't get bred...
I don't have any other suggestions from the "dairy experience" I have had....
Just for ... whatever... you say there is no evidence she is sucking herself... When you have a chance to get her up... get your hand wet with some water and run it over the teats... if they feel slimy on your wet hand... she is sucking and they are drying and you are not noticing her sucking.... but you have to use just plain water on your hand... not like licking your finger to get it wet, then touching the udder/teats...
But I think you might be right with a hormone thing...