Question about sapphire crystal

Hello

Wanted to hear from you before I approach service centre.

My little niece somehow managed to leave a mark on my longines automatic crystal. It does not appear to be an actual scratch on the crystal, might be a light faint mark on the AR coating.

My question is, can the AR coating be repaired ?? Coz I know if I want to get it replaced, I will be charged a bomb.

Thanks
DB