I've never heard someone from the US (where I'm from) use that phrase. I think it's a UK thing, but I could be wrong. But in any way from what I've seen it means she has an attitude with bite, basically, a sarcastic with about her.
It means you are being like a bear.
They actually aren't referring to you at all that's just yardie slang for potatoes.
And well potatoes are vegetables, round, and yellow, hard when not cooked and they have patches of earth and sometimes roots sticking out of the top.
Basically, someone who has a nervy, smart-ass sense of humor.
pretty much this link
The way I have always heard it used makes it seem like a nice way of calling someone a smart ass.