I remember this book I loved in the early-mid 90's about a girl who was able to travel back in time to the 70's and meet her mum (I think). I can't remember the whole story, but I feel like maybe her parents were deceased in the present. The other bits and pieces I can recall...
- She had a crush in the present day, and it turned out that his grandfather was the cause of someone's death in the 70's... and by figuring this out when she travelled back in time, she caused the grandfather's arrest, meaning her present-day crush was never born.
- There was definitely some subplot regarding a cryogenics lab.
- There was a girl in the present day who had "cookie" eyes (maybe they were like cookies with bites taken out of them?), and she never knew her parents, and would frequent a hologram-virtual-reality place in the mall and make-up fantasy picnics and such with her "real" family... In the end, after the past was altered, this girl ended up in the "new" present day with her family rather than being an orphan.
- There was definitely a party that took place on a beach.
- The kids in the present day were all part of some study dealing with mind-control and being able to make objects move without touching them. Somehow this factored in to the lead female being able to time travel.