We know Jennifer the best as the grandmother from the Charmed Ones.
Mostly she is named 'Grams' in the show. She raised the three sisters after their mother Patty died and their father Victor wasn't around.

I didn't find a lot information about her on the internet, I only found the shows and movies she starred in.

Starring Roles

Charmed (1998) - Penny 'Grams' Halliwell (Re-curring)
Nightingales (1989) - Effie Gardner

Guest Starring Roles

Charmed - 'Grams' Penny Halliwell - Witchstock (2004)
Charmed - 'Grams' Penny Halliwell - Necromancing the Stone (2003)
Boston Public - Claire's Mother - Chapter Sixty-Two (2003)
Charmed - 'Grams' Penny Halliwell - Sympathy for the Demon (2002)
Charmed - 'Grams' Penny Halliwell - Happily Ever After (2002)
The District - Margaret De Sica - The Killing Point (2002)
The Agency - - Closure (2001)
Charmed - 'Grams' Penny Halliwell - Charmed Again (1) (2001)
Popular - the real Jody Salk - I Know What You Did Last Spring Break! (2001)
Charmed - 'Grams' Penny Halliwell - Pre-Witched (2001)
Charmed - 'Grams' Penny Halliwell - Just Harried (2001)
Charmed - 'Grams' Penny Halliwell - Magic Hour (2000)
Time of Your Life - Roberta - The Time the Truth Was Told (1999)
Charmed - 'Grams' Penny Halliwell - Witch Trial (1999)
Ally McBeal - Gladys - Only the Lonely (1999)
Charmed - 'Grams' Penny Halliwell - That '70s Episode (1999)
Charmed - 'Grams' Penny Halliwell - Is There a Woogy in the House? (1999)
Family Matters - Blanche Geiss - Lost in Space (2) (1998)
Family Matters - Blanche Geiss - Lost in Space (1) (1998)
Friends - Mrs. Lynch - The One Where They're Going To Party! (1997)
3rd Rock from the Sun - Mrs. Sumner - Fourth and Dick (1996)
Murphy Brown - Mrs. Crawford - Office Politics (1996)
3rd Rock from the Sun - Mrs. Sumner - Much Ado About Dick (1996)
3rd Rock from the Sun - Mrs. Sumner - Body & Soul & Dick (1996)
Wings - Mavis - Lynch Party (1996)
ER - Mrs. Henry - It's Not Easy Being Greene (1996)
3rd Rock from the Sun - Mrs. Sumner - Brains and Eggs (1996)
The Larry Sanders Show - Irene - Hank's Sex Tape (1995)
Party of Five - Carolyn Prousky - The Trouble with Charlie (1995)
Full House - Liz Larson - Desiging Mothers (1992)
Morton & Hayes - Hutn Guest #2 - Society Saps (1991)
Equal Justice - Judge Billings - The Devil His Due (1991)
Designing Women - Ms. Tauber - The Big Circle (1991)
Gabriel's Fire - Connie DiFranco - Windows (1990)
Knots Landing - Woman - Dead But Not Buried (1990)
Knots Landing - Attorney - Dead But Not Buried (1990)
Knots Landing - Woman - God Will (1990)
Quantum Leap - Agnes Stevens - Blind Faith - February 6, 1964 (1989)
L.A. Law - Ms. Gylkowski - Dummy Dearest (1988)
L.A. Law - Ms. Gilkowski - Prince Kuzak in a Can (1987)
Matlock - Gracie Fielder - The Stripper (1986)
Knots Landing - President - Let Me Count the Ways (1980)
Lou Grant - Dr. Roberta Giani - Poison (1978)
The F.B.I. - - The Gopher (1972)
The High Chaparral - Tanea - A Man to Match the Land (1971)

Co Starring Roles

Maggie - owner - The Maris Syndrome (1998)
Little House on the Prairie - Mrs. Hale - No Beast So Fierce (1982)
Little House on the Prairie - Nurse - The King Is Dead (1979)

Movie/Mini-Series/Special Roles

Heathers (1989) - Veronica's Mom
Slumber Party Massacre II (1987) - Mrs. Bates
The Death of Richie (1977) - Elaine