Help with german shep. Behavior?

Ok..im a vet tech of 5 yrs and I have a 2 yr old german shep female spayed dog. the doctor I work for have tried to help with some issues shes having but no success. We even put her on a natural anxiety med to help calm her...no use. I think she needs ceaser but thats not gonna happen. Her problem is first I have four cats and she is obsessed with only one. Shes the only female kitty also. She watches her...stalks her...wants the cat in her mouth..but doesnt ever hurt her. To watch them it's almost like the dog is in love with this cat ...the behavior is never aggresive toward that cat. I just want someone to make sense of it. Secondly she rides in the car almost everyday and if we see a dog she goes completely balistic..i have no clue how to fix this. And lastly...the most serious...she has a house mate a little 7lb jack chi and they get along for the most part and I take her to a off leash dog park often...recently our trips their have been bad. She lashes out at other dogs when they come up to sniff her or smell her while she pees or poops. Also gets upset when dogs she doesnt know comes up to me. I just need tips on how to help her. Ill never give up on her ...most everyone has but not me ...we'll deal with this forever if we have 2...