Can anyone tell me what this plant might be. It is my friend's garden and she doesn't know what it is.
Looks like Heracleum mantegazzianum (giant hogweed), a noxious invasive. If it is, the plant can cause skin irritation, so use caution.
Yep, Heracleum mantegazzianum. Definitely one to be rid of, a.s.a.p. before it starts shedding seeds. And as Eric mentions, avoid contact with the sap - it is nearly as bad as poison-ivy. Useful info here: http://www.sl.kvl.dk/upload/kaempe_bjorneklo_eng.pdf (pdf file)