Anna Nduku fell into the Kandisi river near Ongata Rongai, on the outskirts of the capital, Nairobi. Ms Nduku was responding to the cries of help of a man who was clinging to part of a bridge that was under construction.
The man survived but as she tried to save him she fell into the river. The river was overflowing after a huge downpour that began on Monday.
"I saw her struggling in the water and I tried to save her. I called out to her 'Anna, Anna!'” said Ms Nduku's mother, Elizabeth Mutuku, who was nearby when the accident happened.
"I wanted to throw her a stick to try and pull her out. But the river was swollen and she was being tossed and tossed around and then it swept her away."
Residents of Ongata Rongai say Nduku’s death is just one of many deaths that have occurred in the area over the last two years as a result of the unfinished bridge.
An old bridge was removed in 2017 and the new one has not yet been finished forcing the residents to wade through the water and using stepping stones to cross over.
Ms Nduku's older sister, Maryam Zenneth, blamed the local authorities for failing to finish the crucial link between her village and the main market town of Ongata Rongai.
"Many people are dying and they are sitting and watching people die," she angrily told the BBC.
"They come and grieve with you but do nothing... Today it is my sister, who will be next?
"This bridge is the main highway for kids who are going to school. Why did they remove the bridge to start building another one and they aren't finishing it?"
Meanwhile, the Kenya Meteorological Department (KMD) has cautioned Kenyans to be on the lookout as heavy rains are expected in the coming days.