When Buffy brings home cursed candy, Joyce reverts back to her teenage self. She hooks up with Giles and they end up sleeping together on the hood of a police car!
When children are found murdered, Joyce starts a campaign to rid the town of evil and claim back Sunnydale for the people. She falls under the thrall of a demon disguised as two dead children, and under their instruction alomst burns Buffy and Willow at the stake. The other scoobies manage to get there in time and break the spell, with the true demon revealed, Buffy impales him on her stake and kills him.

When Buffy goes off to college, Joyce is left home alone, not alot is known about her activities at this time, we presume she works and has coffee afternoons with her friends,
When Faith turns up at the Summers' home, she holds Joyce hostage, until Buffy arrives to save her.
When Dawn is intergrated into the show, she fits in with ease and becomes Joyces favourite daughter, however, when she collapses in the kitchen things start to look bleak. After rigourous testing, its discovered that she has a brain tumour, causing her to act and say things totally out of character. Its in one of the times that she realises that Dawn isn't actually her biological daughter, she turns to Buffy for advice and Buffy explains the situation to her.
On temporary release from the hospital, an extra terrestrial named Ick, hitches a ride home with them and tries to kill Joyce. Thankfully, between Dawn and Buffy, they manage to kill it, with a little help from Spike.
Joyce returns to the hospital for major brain surgery which proves to be successful. The Summers family return home to help Joyce recover. After a short period of time, Joyce starts going back and out she meets a guy. After their first date, he sends her flowers. Buffy arrives home and sees the flowers. Buffy finds Joyce collapsed on the couch, the realisation that she has died hits Buffy hard. Its revealed that she suffered a huge anurism in her brain, causing her death.

Dawn casts a spell to bring Joyce back which proves successful, although it wasn't determined if Joyce was the same person she was when she died, as Dawn broke the spell before anyone could really see her.

Joyce was finally laid to rest in peace.