Walking Troubles :S

Question
Hello, I'm in desperate need of advice! We have a 8 month old female Great Dane called Brook and she is wonderful! So loving and friendly! This biggest trouble we have with her is teaching her to walk... With another dog! She's brilliant on her own I can walk her fine I use a semi-choker and a 20" leash so if she pulls a little or tries to change direction I'll give a little tug to create the "zip" noise to grab her attention and correct her and it works fabulously! But we have a 4 year old Jack Russell called Jess and she sends Brook wild! I struggle to walk Brook when my partner walks Jess because all she wants to do is run around like mad because Jess likes to bark which makes her go mad. Then I'll walk a good 20 meters ahead but she just wants to turn around to watch what Jess is doing the tug and correction will not work at this point she just doesn't want to know! And then I'll try walking Brook 20 meters behind Jess and she started sprinting, I had to let go of her because I was just about to be pulled right across tarmac! The pair of them are fine in the house they don't bother each other! And another thing when Brook's running in the field she keeps running and trampling over Jess and sending her flying and did it to a strangers little dog too! She knows they are there in front of her I really don't know why she does it but I am at the end of my tether with her and can't bring myself to take her out because I just cannot control her :( PLEASE PLEASE HELP!!! Thanks for reading my very long plea!!

Answer
What type of collar or training device are you using for Brook?
What type of collar or training device are you using for Jess?
What are the lengths of your leashes?
Does Brook now how to heel when you are walking her one on one?

Please provide me with more information so I can give you a better answer