My experience is Momma accepts them
if the timing is right....i.e. not a week into sitting...but around the time hers would hatch or shortly thereafter. However, if hers hatch...it needs to be IMMEDIATELY. Some will accept added chicks later, some won't. I had a great hen that I 'ruined'. She hatched 5, and local TSC had chicks on sale (starting to get wing feathers, so had to go) Hers were 3+ weeks old, bought 23 chicks 2 wks old for 10 cents each (some were to go to my neighbor, but in a couple days). She accepted all 23 newbies! (The look she gave me was " Oh, S*#t!)

However, she has never gone broody since...and I've kept her...she is almost 5 years old, and she went broody her first year....so following 3 years, nothing...I broke her

She was such a good Momma, too.