I turned the wife into a Vampire and now I can’t find her

The walking out after saying "I do" part is normal. Lives in Skyrim are too short for drawn-out ceremonies. Spouses will return to their daily routines, not necessarily their houses, until you move to your own property, in which case they'll (usually?) stay inside.

There are some conditions under which a spouse may attempt to kill you. For example, Mjoll the Lioness will attempt to kill you if your murder of Aerin becomes known. Even though the creep moves in with you if you leave Riften.

There are chances where the follower is stuck in a position, could be this or also in fighting stance.

Normally the best way is to load a saved game before this happened instead of continuing to play since there is a chance that this is not possible to fix.

Other options would be to do something that resets the position. I would try to use the fus-roh-dah on her to throw her over. She will then have to get up again form the floor.

The change of stance needs a trigger. So to sheath the weapons or to get up from crawling, there needs to be a change in situation that causes the trigger. If the system overlooks one trigger, the follower is stuck in the stance. You have to re-initiate a trigger to change the stance again. I am not sure what kind of attack would work since I am not sure how the follower would normally react to an attack while crawling. However a fus-ro-dah normally topples players over completely and then initiates the "get up from the ground" movement, and I am quite sure that if you manage to topple her over, she will not get into the crawling stance.