She may not appear very dominant but she will be and the others will all know her position and their positions, thereby she may not feel the need to enforce it with lots of dominant behaviours. It doesn’t mean she, nor the dominant of the other herd, would be prepared to step down and accept a lower ranking position, and this is why merging two established herds of adult sows is a tricky thing to achieve.
All you can ever do with a bonding is try is on neutral territory and see what happens.
If it doesn’t work and you’re committed to the second herd, then you will need to split the shed in half so they can live side by side.