Has anyone experienced the vanishing twin syndrome?

My sister found out she was pregnant 2 weeks ago (we're both pregnant at the same time...so excited!) and during her ultrasound she was told that they might be having twins! But she was warned about vanishing twins syndrome so was curious to see if anyone else had experienced this.

Apparently it's when a woman is originally carrying twins and one of them doesn't stick and gets reabsorbed back into the body. After doing some research online, it looks like it can be fairly common and usually happens before the 1st ultrasound (at around 8-10 weeks). So it could happen without knowing it, unless you get an early ultrasound.

I'm so scared for my sister (she wants twins so badly) so wanted to reach out to the Hellobee community for advice/information.