Fantastic pictures Tdierikx, you should do this professionally (if you don't already).
Yes, that certiantly is some dominant behaviour from Mbeli. She has clearly had the advantage of being in the new group first, being the first female to give birth (additional attention/protection from Kibale) and now her baby is mobile, she can put him down and engage in conflicts without fear of him getting injured. Perhaps Frala, is wary of provoking conflict when she has a newborn clinging to her, and she will become more assertive six months down the line, when she is physically able to?
Do you know much about the hierachy of the previous group? I understand Mouila was the favourite of Kibabu, did that automatically make her the alpha female? Taronga said Kriba would sometimes assume the role of second in command to Kibabu (ie. when patrolling the exhibit etc.). Frala was obviosuly an outsider, but the presence of her adolescent son, Fataki, gave her the oppotunity to take a swipe at Mouila etc. I think Fataki got a bit too big for his boots towards the end.