Becky, 16, was killed by her step-brother during a sexually-motivated kidnapping at her home in Bristol on 19 February last year.
Her aunt, Sarah Broom, said relatives plan to mark Becky's "big birthday" - her 18th - in June with a party.
They also hope to start a charity to help those whose relatives go missing.
Nathan Matthews was jailed for life for Becky's murder, to serve a minimum of 33 years , while his girlfriend Shauna Hoare was given a 17-year sentence for manslaughter.
Ms Broom said the family had struggled to "return to normality" after her killers were jailed.
"It was really strange finishing the trial, you kind of miss it because that has been your fight and then when it's done, you're kind of lost," she said.
"Where do you channel all that now? We've tried to put it into events, fundraising and just trying to build happy memories as well.
"We threw her a party for her 17th birthday. We went to her grave and sang Happy Birthday."
Becky's uncle Sam Galsworthy said: "It's destroyed us all but it's also brought us closer together. We're closer than we've ever been I think."
The couple said community support during Becky's disappearance had been "amazing", and said she "couldn't have had the funeral or headstone" without it.
Becky was reported missing on 19 February 2015 and her remains were found in suitcases in a shed, in Barton Hill, nearly two weeks later on 3 March.
Ms Broom spoke about the "desperation" they felt during the search for their niece, and said the family was aiming to set up a charity in Becky's name to help others whose loved ones go missing.
"We found the expense of just poster printing and arranging our own searches, we're just an ordinary family and we didn't have the resources.
"Our aim is to make it easier for another family," she said.
The family of murdered teenager Becky Watts has vowed to mark the "sad milestones" of her life with "happy memories" a year after her death.