Translation...

Usually I do well at understanding Miss R's dialect.  After a late start talking, she now speaks very well (and incessantly), but once in a while things do get lost.

Miss R:  Pwetend it was a sew-er sire hoe-se.
Mama:  A what?
Miss R:  A SO-er sire hoe-se.
Mama:  A sew er shire horse?  (Thinking, a horse that sews?  What is she thinking?)
Miss R:  NO.  A SO-ER sire hoe-se, that sews twicks.

So sew equals show, and the tendency to shout when people don't understand what is being said to them evidently begins at birth.

Oh, and when Miss R is pretending to be an animal, which she usually is, she refers to herself in the third person, thus the "pretend it was a shire horse."