Newsflash: Can “under contract” be cancelled?

So I just found out that my retired mother (81) put up for sale the home we lived in from my early teens-20s, after my parents got divorced. She, my older brother & me all lived there. I’m 51 now. It was the entirety of my junior high & high school years. All my friends lived in the neighborhood. I have so many memories of many, many, many family get-togethers, fights with my older brother (who passed 25 years ago), and neighborhood high jinks. Anyway she re-married and moved to another state, kept the property and has been renting it out for years. I only found out a few days ago that my mother put it up for sale (when I Googled it & other family homes just out of nostalgia), then I checked again today and see it’s “under contract”, for barely two days now. I immediately emailed & texted my mother asking her not to sell (she’s asleep due to the time difference). What I’d like to know is, is she obligated to go through with a sale if it’s under contract, or can she pull out without any penalty? (It’s in the state of Virginia if it matters). I’ve heard there’s a contract involved when you list with an agent, but beyond that I don’t have any idea about the process. As far as we know she’s still very healthy, but she said she’s making some changes to her “end of life” plans. I don’t know if I’d move back to that area and live there again or not. But I feel very attached to that house and do not want to see it sold! Also she has a grandson and a great-grandson (my nephew and great nephew), so it just seems like we should keep some property in the family. My feeling is, why sell real estate if you don’t have to? So, can the sale be stopped?