The time on the clock looks like it says 8:50 so she may be the first one there and knows nobody could walk in. At first I thought she was adding some milk because it was almost finished but judging by the angle she tilts the carton it appears to be 3/4 full. Therefore this is more of a revenge plot or friendly prank than a charitable donation.
No doubt this could be fake, everything has been faked on the internet.
Points for creativity though.