Learn Turkish: Annem kermes için hazırlık yapalı tam bir yıl oldu. - It has been exactly one year since my mother prepared for the charity bazaar.

The suffix -(y)alı (or -(y)eli) means 'since [doing something]'. It attaches directly to the verb root. Here, yapalı means 'since she made (preparations)'. It is commonly used to express how much time has passed since an event occurred, usually followed by a time expression and oldu or geçti.

Could I use yaptığından beri instead of yapalı?

Yes, you can! Hazırlık yaptığından beri also means 'since she made preparations' and is perfectly grammatical. However, -(y)alı is a shorter, very natural alternative specifically used when stating the amount of time that has elapsed, as seen here with tam bir yıl oldu.

Why use hazırlık yapmak instead of a single verb for 'prepare'?

In Turkish, the compound verb hazırlık yapmak (literally 'to make preparation') is often used for organizing or setting things up for an event. You could also use the reflexive verb hazırlanmak (to get ready or to prepare oneself), making it kermes için hazırlanalı, but hazırlık yapmak emphasizes the active process of making arrangements.

I see the -lık suffix in hazırlık. Is this related to the time duration grammar like bir yıllığına?