I stained my grandmother's curtains with a sauce that containedmayonnaise and other stuff, don't know exactly what... The deal isthat the grease stain is quite big and I don't want her to noticebecause she really cares about those curtains. I managed to hide thestain somehow by repositioning the curtains but it won't last long.What should I use to clean them up? 

Waiting for your answer, thanks!