Sun conjunct MercurySun conjunct Mercury confers creativity and the ability to act in all things denoted by Mercury, especially in ideas, work, and friendships. (Communication in all its forms is one of the things denoted by Mercury.)
This aspect shows a tendency to enforce ideas and decisions with willpower. However, it also hinders objectivity in self-analysis by contributing to a very close identification of mind and ego. This makes it difficult for natives to view themselves impartially, or as others see them. (Sounds like she has the same problem as Keith).
These natives are endowed with mental stamina and have a great deal of mental energy. If Mercury is conjunct the Sun within an orb of 1/2 to 4 degrees, Mercury is said to be "combust", creating a condition in which the lines of thought communication are overloaded with solar energy. Then a breakdown of communication and thought processes occurs, which can be compared to the way fine wires in an electronic component are destroyed if they are subjected to an overload of electricity. When this excess energy overheats the mental processes, a more or less momentary mental blind spot results.
(Katy’s conjunction is separated by 4 degrees, with her Mercury at 29 deg. Libra, and her Sun at 2 deg. Scorpio).When Mercury is conjunct the Sun within less than 1/2 a degree or 30 seconds of arc, Mercury is said to be "casimi." This position, while having some of the same difficulties of the "combust," is also a "dignity"; when the alignment of wave patterns is so perfect, the solar energy is modulated by Mercury and becomes a perfect carrier-frequency for the mind. In other words, the will becomes a vehicle for mental expression.
When the conjunction is in Gemini, Virgo, Aquarius or Libra, this confers high powers of intellect. (Katy’s conjunction is in Libra, and Mercury, at 23’ seconds of arc, less than the 30’ seconds for a “combust”. Without a time of birth, this cannot be determined with any accuracy, but she seems to function well enough not to be considered “combust”. But I don’t see a powerful intellect. Perhaps that will develop with age).