Some legal advice needed...

I can guess the only way to (legally) get the money back (ut's about a grand...) is to get to the small claim court...

Small claims court is the way to go, you can do it online in under 5 minutes.

I'm just wondering:
how effective it can be?

Effective. I would tell her what you are going to do first, give her a few days to respond (no more)- it will cost you some money to lodge the claim, which you get back (it is added to the money she has to pay).

how much time will I have to spend after the claim?

This question is much too vague for my suspiciously aspergic brain.

of course I don't have her new address but know where she works and know a family address..would the work address be enough for the claim or it needs to be a home address?

Pretty sure the work address should be good enough, you will need an address for the claim itself and - (if she looses and does not pay - or does not contest and does not pay) - for the bailiffs if you then take out a warrant

It's all very straightforward.

• listen to what Tommy said, write everything down, you probably won't need it, but best to cover yourself.