I've been a victim of domestic abuse and it sounds like whilst op is absolutely well-intentioned, she has no clue about the complexity of a relationship where abuse is involved.
There are myriad reasons why her friend doesn't just 'leave'. She may not want to admit she is being abused. She may not want to admit even to herself she is being abused. She may think op is being an interfering old bat (whilst questioning if there is any sliver of truth that op thinks she is being abused).
Once a person recognises that there is abuse, there may be many many reasons why she can't leave. Or maybe doesn't want to - risk to kids, breaking the family, cultural reasons, finances, risk that if she does say she's leaving that the abuse will escalate. Maybe all of these.
It's so easy to say to someone 'youre bring abused you should leave'. Really easy.
But getting out of that relationship - with kids, finding new accommodation, new job, finances, risk of further and intensified abuse - is overwhelming. And takes years to get into a new normal, especially if DC involved, divorce process is costly and protracted, finances complicated especially if selling a property
It took me years to leave my relationship because of all the above, and more. The abuse continues via the DC (he took me to court 3 times regarding the DC and finances, I came out on top despite his insane requests and allegations), I had to get a judge to order the sale of the house 5 years after I left, and he's made malicious allegations about me at work since.
All the while my parents were utterly ashamed I'd broken up the family - despite documented abuse and police reports
It's nowhere near as easy as 'she should just leave'