。
She visits her grandmother on Saturdays.
Literal
She [topic-は] Saturday [on-に] grandmother [object-を] visits.
A clean, polite sentence using ます form. おばあさん is the standard polite term for 'grandmother' (or any elderly woman). 訪ねる is a more purposeful word for 'visit' than 行く — it implies going to see someone specifically, not just going somewhere.