None But The Gulls by Blodwyn Smith

Shayna Richardson gets more than she bargained for when she offers to help Mary De La Ray cope with her sullen, self-pitying daughter, Lorna, who is wheelchair bound after a riding accident.
Despite crossing swords with Jared, Mary's wealthy son, Shayna is attracted to him and intrigued by the mystery surrounding the car crash in which his wife died, leaving her friend Jenna traumatized and unable to recall the accident. Why has Jenna such a hold over Jared? And why is she instantly antagonized by Shayna's arrival?
Dispite Lorna's progress, eventually Shayna can take no more and drives away leaving no address. Jared eventually finds her and brings her back only to find Jenna has desperately tried to get his attention again.
Jared had always refused to take Jenna to his second home, Cragsend, but when she hears Shayna has been there with him she is incensed and hatches a deadly plan to lure her away.

A bloody encounter takes place - will a tragedy be averted by the intervention of a young farm hand?