For pronomial use, Siúlann sí go dtí é could be used for “She walks to where he is” rather than “She walks towards him” — that is, if his location is her destination rather than he being her destination.
For a general destination, go dtí requires a location that has a definite article; go could be used for a location without a definite article.
Leis can either be a form of the preposition le (e.g. when directly preceding an article) or a prepositional pronoun that means le + é. The preposition can be translated by several different English prepositions, depending upon the context, just as the English preposition “for” is translated into Irish in several different ways, depending upon the context.
Chuige is a prepositional pronoun that means chuig / chun + é. (It’s also an adverb that means “at all”.) The preposition chuig / chun can also be translated by different English prepositions.