My friend has this grass growing in her shady flower bed. I was sure it was a weed with how its completely taken over the entire bed. But nothing I've read online (now that I've identified it) describes it as anything other than an ornamental grass. Does anyone else have problems controlling this?

The flower bed was already established when she moved to RI 5 years ago & she's not a gardener, so the bed has received little to no care. Until now.

Thanks for your time!