i agree with whats been said...
it sounds like a dominance issue, she came from a byb situation correct? so shes probbaly used to fighting for her dinner and having to realy stand up for herself...
now shes in a new situation, old habits die hard.
being shes also pregnant and still in heat (7-14 days) shell also be the equivalent of pms'ing.
once shes spayed the doninance Should die down, for now you need to assert your dominance, if she goes for another of your dogs step in and tell her no, she'll soon learn your in charge...make sure theres always enough food to go around and it might be worth feeding them in seperate areas for now, just go slowly, shes had a hard life, itll take her a while to settle in.
the leg lifting is common in intact and dominant females, the one who pees highest is the one in charge! lol.
and welcome aboard Ruby