。
She's planting roses in the garden.
Literal
She [topic-は] garden [at-で] roses [object-を] is-planting.
Note the particle で rather than に — 庭で marks the garden as the location where the activity is happening (where she's doing the planting), while 庭に would mark it as the destination (where the roses end up). Both particle choices are natural; the nuance shifts slightly from action-oriented (で) to result-oriented (に).