Trouble in Bee city

Last Saturday I checked the hive to see if everything was okay and found a queen cell (top middle). This is worrisome. A queen cell means that the workers are not happy with Queen Isabella and want to replace her.
At first we thought Isabella was killed or injured or missing, which would cause the workers to make a new queen, but we found her in the hive, so it is a confusing state of affairs.
IF Isabella is 'failing' then there are two options. Either let the bees sort it out themselves, or buy a new queen and re-queen the hive. We decided that since we don't know what we are doing we should make the bees some sugar-candy and hope they can sort things out.

We will watch the hive closely and if there is still worry by mid-June we will re-queen. Until then I hope they can settle the matter among themselves.