Ahhh.....now I see what you guys mean. I think you are onto something with the gypsophila! Here are some more pictures. If it is a Gypsophila, it makes me want to collect seeds, weed or not! It's pretty, and it's Gypsophila (we think!)...
(The description for smartweed scares me, so I will probably quash that plant before it goes to seed, even though it is very attractive, in my opinion.)
Here is a picture of nearby baby's breath....cousins in the same pot, perhaps?
Edited to add: I misspoke about the neighbor flower's identity....it is sweet alyssum. My brain just doesn't work lately. They do say that sweets addle the brain and give you 'brain fog'...perhaps I can blame the plant! LoL