Going by LAW is the biggest mistake you will do in your life.After trying very hard by consuming your personal efforts If nothing works at all then keep option open to go by LAW .
There are always small things ,which without proper attention and resolution ,gets converted to LETHAL PROBLEMS for family life.The best option is to take initiative by HUSBAND and WIFE to discuss and resolve it accordingly.Not only law can resolve problems.
Dear, I am of this opinion that first of all try to accept your faults very honestly.Acceptance makes person transparent.Do not overstress yourself as well.
Keep your head always cool while talking on phone and behaving with her .It may present you wrongly.Its a bit hard,coz you must be going through tremendous pain, as you are unable to meet your child.Its really very painful.I understands coz I experienced it myself.But we have to accept whatever comes in our path while living life.BE STRONG FOR YOUR CHILD.
Try to discuss with her , bring her back keeping your as well as her dignity.
If this does not work,and my guess is that her parents must be unsocialised,selfish and VERY careful about her.At least may be only showing for their selfish goal.That goal might be to keep her with them to take care of them.If your wife dont have any brother then above VERY CAREFUL becomes VERY VERY CAREFUL.
Anyway these parents must have kept her under their strong influence,her every decision must be taken by them.if yes it'll be very difficult to cross their strong influential fence.
Do it with the help of her closest friend,common relative,professional collegue,give preference to WOMAN to mediate.Consistent 3-4 interactions may soften her stand.Continue contacting her.Dont cut off communication.
Then might be things will crawl towards you positively.
Keep confidence level high.Whatever you will do ,do it HONESTLY.
It will deliver the RESULT.
:)