。
She's putting on toner.
Literal
She [topic-は] toner [object-を] is-applying.
化粧水, literally 'makeup water,' is the Japanese term for facial toner — the watery skincare step applied after cleansing and before moisturizer. つける ('to attach, to apply') is the standard verb for applying liquids or topicals to the skin: 香水をつける ('apply perfume'), 薬をつける ('apply medication'). Skincare vocabulary in Japanese leans heavily on transparent compounds — 乳液 ('milk-fluid' = milk lotion), 美容液 ('beauty-fluid' = serum) — making the category easy to expand once you know the building blocks.