Oh, I think very many good parents treat their kids roughly, more often than they'd like to remember/admit. A quick shake by one arm, the hand that slaps the back of a knee, the face that screws itself up and shouts, the hands that 'firmly' sit you in your seat, lifts you off your feet and firmly put you down somewhere else, grip your arms slightly too tightly, pats the newly nappied bum a tad too firmly....
Lots and lots of little things.... no one a big deal and all perfectly understandable. I'd even say that roughly handling toddlers, 10 month olds etc is and has always occurred, all parents will have had at least one moment where they pass that line.... momentarily.
The vast majority of occurrences are wholly harmless, seldom occurring actions. And, as I said earlier, every parent will go through it, over and over again. No-one gets out of childhood without a parent losing it... often only the parent remembers, thankfully.
The women being described may or may not be a serial offender. Either way would have sympathy for her. No-one wants to be like that with a small child. There has to be something that isn't being coped with. There has to be a something a someone could do to help. Hopefully she has that someone!
But I wouldn't judge her on what the OP saw and heard.