RORY (looking at photo of Sherry): Nice looking lady.
LORELAI: Mm hmm. Like a young Tammy Faye Bakker.
RORY: But prettier than that.
Tammy Faye Bakker, born Tamara LaValley (1942-2007) was the ex-wife of television evangelist Jim Bakker (born 1940). She and her husband ran a televangelist program called the PTL Club, founded in 1974; it was dissolved in 1989 when Jim Bakker was convicted and imprisoned on indicted on numerous counts of fraud and conspiracy. Tammy Faye divorced Jim in 1992, and married Roe Messner, a church building contractor (so by this stage she was actually Tammy Faye Messner).
Tammy Faye was known for her eccentric and glamorous image, and her views which often diverged from mainstream evangelical Christianity. For example, she supported the LGBT community, and reached out to HIV positive patients at the height of the AIDS epidemic. She was diagnosed with colon cancer in 1996, so was already terminally ill when this episode aired.
It is unclear what age “young” Tammy Faye Bakker was that Lorelai believes Sherry resembles. Knowing what Sherry actually looks like, perhaps when Tammy Faye’s hair was brown, before she dyed it blonde. That would have been in the 1960s, when Tammy Faye and her husband Jim had a puppet show on a Christian TV network.
The viewer may decide for themselves whether Sherry looks like Tammy Faye Bakker at any age, but I personally cannot see any strong resemblance (I can barely see a weak resemblance). I’m surprised that Rory doesn’t disagree any more strenuously than by saying Sherry is “prettier than that”, and can only think that she walks on eggshells when it comes to her mother’s jealousy over Sherry.
I’m not sure how Lorelai’s frame of reference for picturing a young Tammy Faye Bakker is in the 1960s, before Lorelai was born. I find this whole reference quite confusing.