Complex sentence: She may be best known as Penny "Grams" Halliwell on The WB series "Charmed", where she starred as the spirit of the Charmed Ones' grandmother and the tough-as-nails matriarch of the Halliwell clan.
Split into simpler sentences: She may be best known as "Grams" from The WB series, "Charmed", where she starred the spirit of the Charmed Ones' grandmother. There she played the tough-as-nails matriarch of the Halliwell clan.