What were her living circumstances at the time she got married? Were her parents alive and did she have any siblings who lived close by that could help her? Did she have any 'illegitimate' children that needed a father figure to support them?
When I was looking into the background of my 3x great-grandfather's second wife, I noticed that when she got married her father had recently died, all of her adult brothers were either dead or had moved elsewhere, and her mother and three sisters had recently all been admitted to the workhouse. It seems that by marrying my 3x great-grandfather, a widower with five young children who was nine years her senior, she was spared the same fate.
In desperate times, a woman may have had no other option but to get married to the man who was most immediately available.