。
She's watering the flowers.
Literal
She [topic-は] flowers [to-に] water [object-を] is-giving.
水をやる is the everyday way to say 'water (plants, animals, etc.)' — literally 'give water.' The verb やる (here in its donative sense) is the casual cousin of あげる, used for giving to plants, animals, or social inferiors. To Japanese ears あげる feels too elevated for plants, so やる is the right register here. The flowers, as recipient, are marked with に. 水をやっています keeps the polite progressive register: she's in the middle of doing it.