What do I suggest for a 3 year old who is hitting, biting etc?
Disclaimer: I wouldn't suggest it to her, as its her child, etc etc but if it were me, I would take the child aside, get down to his level, and say "we do NOT hit. If you hit again, we will go home. Do you understand?"
That's his warning. Then, if he hit again, I would put him in the car, tell him that I told him that if he hit that we would go home, and that because he hit again, we are going home. Then I'd go home. Child would very likely be suitably remoresful.
Then the next time you go out, you pep talk them in the car - "remember what happened last time when you hit? We went home didn't we. You must not hit any of your friends or we will have to go home" etc etc. I have found by this age that is very effective. Its not to say it will be on her child, but I suspect it will be more effective than what she's doing, which is completely ineffective.
You might have to turn around and go home a couple of times, but I'd hazard a guess it wouldn't continue long.
For me, personally, I go to soft play or someone's house for a play date for my child's benefit, not mine. If they go round behaving like that, I dont want to be there and others possibly dont want them to be there anyway. So I would be killing two birds with one stone by getting out of there whilst driving home the message that if you can't behave when you go out, you dont go out.
Difficult if you have a younger/older sibling with you who is also benefitting from the outing - as they would then get punished for no reason - but this is not the case with the friend I am referring to.
That's what I'd do, anyway! Its up to her what she does - but its getting to the point where we are starting to distance ourselves and spend less time, as its pretty distressing for the injured party and its not getting any better, its getting worse.