Submissive new addition

We have three dogs at the moment. Our rescue entire neopolitan mastiff of 8/9yrs, a foster female speyed mastiff cross 20mths and a rescue unspeyed female dane cross 7/8yrs.

Ted was a lone dog (after losing our two staffies) until the foster girl came along. Even though she was very wary of dogs she took to Ted as he is quite a benign type dog. He has only ever asserted his dominance (a lip quiver!) once when she got excited in play and mounted him. He didnt growl or touch her but she knew she had done wrong.
Apart from that no problems.

In comes the last girl. As soon as she arrives she engages the other female in play, making firm friends almost immediately, but ignores Ted.
She never does anything (visibly to us) to Ted that we think would upset the apple cart but we've had a few occasions when she appears to be very wary of him and will stay as far away as possible to him. Or he has growled at her or appears to be 'watching' her and her movements.

She's never done the normal smelling thing with him but has tried to play a couple of times with him but stopped almost immediately (Ted doesnt seem to know much about playing with other dogs but he tries his best bless him!)
She only seems to know one way of meeting strange dogs too, by play bowing and trying to engage them in play.
The group seems destabilised by her presence, is it her submissiveness? And how to help?

Some dogs like each other, some don`t. Some dogs like to play, some don`t. Same as kids.
I assume you`re going to get the new girl spayed? Otherwise you`re going to have a problem.....