It was daylight. There were people walking. It would be exceptionally Risky for someone to let's say murder her. Risky that someone else came along, she screams etc. Leaving the phone on, and in the bench, also would be weird.
Really, foul play seems much much more unlikely than an accident
Unlikely but not impossible. I think it was Ted Bundy who used to feign a limp in broad daylight to appear non-threatening, and kidnap his victims.