I looked up suicide stats for the UK today and in 2021 around 6000 deaths were recorded as suicide and only 5% were from drowning.I'm not disagreeing with you but in terms of statistics, I'd be interested to know what the stats are of lone missing single female, married with children, found dead after suddenly disappearing from usual daytime routine and leaving her possessions and un-tethered dog in a public place. Would that lean more towards an altercation / mugging / sexual assault and murder -or- suicide?
In terms of suicide, jumping in a river would not seem like a very effective method - I've said this on here before but most women would not be too mortified at the idea of being found alive but in a state of disarray very close to one's children's school and home to try such a method.
JMO MOO it depends what else is in the equation for example some people try to take their own lives by drinking toxic fluids such as household cleaners or weedkiller but those substances are so painful they often do something spontaneous and erratic.
Conclusion this very improbable as well, but less so than an accident