She wouldn't remember anything about Riann but if she were to be near her she would feel very threatened and likely go into an instinctive defensive state. she wouldn't know why but she would have this terrible feeling that riann is dangerous and shed struggle to remember why with no luck. serena doesnt usually label people as bad unless they did something significant so if riann got too close and she felt like riann was closing in she would likely revert to her feline instincts and lash out starting a fight.
She can remember how she feels towards people, just her amnesia is mainly affecting her ability to recall events and basic facts she was told such as names and things of the like.