That would not be correct in British English. The past participle is "shown" or (rarely seen now) "shewn". See http://www.verbix.com/webverbix/English/show.html
"I showed her my house" would be okay.
The article you cite doesn't seem to deal with the point. The only mention of the participle is of "shewed" as an obsolete form (and I am not sure that is correct anyway).