
In addition to what the others have said...
First - build confidence. Confidence is your building block for everything else.
Secondly - do NOT think 'how do I stop this behaviour'. Instead, think 'why is this behaviour happening... would would I rather she did... how can I make that happen'.
So - to apply that to your immediate situation:
Don't think 'how do I stop her following me about' - think 'why is she following me around' - the answer is, shes insecure, everything is new. If you prevent her from doing this you will likely cause a bigger problem, so the crate isn't the answer.
Let her follow you BUT - make a point of inviting her if you want her to come with you, and therefore talking to her whilst you do whatever you are doing, rewarding her randomly (fuss, praise, scritches, food, whatever SHE likes best), and also sometimes make a point of NOT inviting her to come with you, and therefore ignoring her presence entirely.
If you are consistent with this she will learn that when you invite her, its good - when you don't its boring.
You can (though I would wait a week or two!) push this a little to make your point clearer - set up situations where for five to ten minutes you will flit back and forth from one room to another - break down a simple task such as making a cup of tea or coffee into ten stages or more. As you move from one room to the other, keep half an eye on her, if she starts to settle in one room, move on.. as she starts to settle again, move on. THe point is that you haven't invited her, you ARENT staying in the other room that long, and its REALLY tedious and annoying to keep following you, settling down, only to have to move AGAIN.... you want her thinking 'darn it, won't my person just stay still!'. YOu MUST ignore her whilst doing this and remember that ignoring means no speaking, no touching and no eye contact - pretend she isn't there!
After a few weeks of doing this a couple of times a day, then introduce a new element - motivation to stay in one place whilst you do this 'fakey' flitting about - the ideal is a large raw bone, but a large food stuffed toy will do, the proviso is it must NOT be comfortable or easy to carry around - it HAS to be so big and so rewarding that she does not want to leave it, and she cannot carry it with her. Then repeat the flitting about, but this time she has her bone and so now the choice is 'follow the boring person who is pratting about back and forth and will ignore me - OR.. stay here with this delicious treat..'
If you can do all of the above, you will very quickly have a dog who is confident about staying on their own in another room, and thats your foundation for her being ok when you are upstairs, out of the house, actually out properly ... etc.
The more things she figures out for herself the better, so learning to be ok about being left this way is MUCH more effective, and kinder to the dog, than shutting them somewhere and forcing them to accept it.
When it comes to other dogs when she is on leash - again instead of 'how do i stop this' think 'why'... Why is likely because shes on lead, thus she is trapped, shes also a terrier so preprogrammed to warn scary things away rather than shy away herself.
Forcing her to get close, to 'get over it', or to prove its ok WON'T work - instead do the opposite, avoid. Demonstrate to her (because after all you can;t explain..) that YOU will take evasive action and create the space s he needs BEFORE she feels she must react.
In effect that means crossing the road, turning around and running away, hiding behind parked vehicles, choosing quiet locations or quiet times of day to walk her.
You might well find that as she settles with you, and you do the above, these problems become insignificant pretty quickly, as they may be largely to do with being new to you and your home, so don't worry just yet that she has any serious issues.