"She bought a new lounge."
Translation:Prynodd hi lolfa newydd.
"Mi" is an untranslatable verbal particle (In this instance- it can also be a form of "fi" but lets ignore that for now.) It can be used with any person plural or singular. In many areas of Wales (most actually) neither it nor it's southern counter part "fe" is used and therefore it is optional. It's purpose it to basically convey that something is happening. Note it's not used in the negative or the interogative. Don't worry too much about it.