[SWHouston]

MM,

I wouldn't just set this aside as an accident....

Is your yard secure ?
Could there have been a dangerous transient animal move through it
and leave their scent ?

I'd go out and check it out thoroughly, look for tracks, something
may be scaring her, and she doesn't want to leave the house.

In the mean time, put Paper/Pad right in front of the door that lets
her out to potty. That'll keep her going in the normal direction for
that, until you figure this out. Be sue to use a good scent
Neutralizer on the area she pottyed in, where that won't
be a reoccurring attraction.