A simpler explanation might be that it's a mangled past perfect subjunctive.
The subjunctive forms look too much like an ordinary past tense
"your momma's so stupid that when the doctor told her to take a urine she wished she HAD studied harder"
so they are slowly being replaced by a simplified syntax where WOULD forms every subjunctive
"your momma's so stupid that when the doctor told her to take a urine she wished she WOULD HAVE studied harder"
or
I heard this for the first time in a freshman lit class. Despite my descriptionist sympathies I very nearly had a stroke.
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