Looks like American pokeweed (Phytolacca americana). Yes - berries and other parts can be poisonous.

Some people make poke salad out of it. I like how they look in garden but in some soils I here they can be some what vigerous and multiply. They are not that vigorous where I live.

Pokeweed leaves MUST be well cooked to make them edible. They are poisonous raw. I think when you boil them, you need to change the water a few times to fully eliminate the poisons. This isn't nice stuff.

Pokeweed leaves are also toxic to animals. Berries less so, and are a food source for many.

Thank you! Is it more likely a weed that just popped up or something that would be bought in a nursery?

Likely popped up - it's a common bird/squirrel/etc gift in our Dallas neighborhood. Seeds probably available somewhere, but I've never seen plants sold in nurseries. An attractive native plant in some ways. Whether or not it is a "weed" kind of depends upon whether you like it.

Edit - they will get rather large with a fleshy tap root that makes them harder to remove over time . Also, those seeds will go somewhere if you don't remove them.... which would be another consideration if they volunteer easily in your mom's location.

It was probably bird-planted. While the berries are poisonous, birds are able to eat lots of less-than-edible berries. Seeds often pass through unscathed and come up pre fertilized. While Pokeweed can be purchased online, I've never seen it in a local nursery. Of course, I may have just missed seeing one.

The ASPCA lists the plant as poisonous to dogs. The dog has to eat plant parts, and the first symptom would be vomiting and stomach pain. More serious symptoms you might notice are breathing issues and tremors. I'm guessing that a dog that tasted this plant and got even slightly sick would stay clear of it from then on.

Thanks, everyone. I called her and told her to dig it up. Can't take any chances with the dogs eating it even if it is a nice look weed.