Hi
This cyst is age related most of the times.
I hope she has no pain or any other symptoms.
Till the time it’s a simple cortical cystitis nothing to worry. When the cyst size increases then it causes pain, that is the time you might require to go for any intervention/ surgery.
Also, the exact size and type of cyst you will get to know after doing a CT scan when anything alarming comes in ultrasound
So for now, it doesn’t seems to be.
Next Steps
CT urography if size increase causes pain/ any alarming finding in ultrasound