also re the pension plan, if it's a work pension plan, that's fairly straight forward, i used form 8833
the important thing is to learn the pitfalls so your wife avoids any future pitfalls. There can be problems with investing in Isas, foreign mutual funds etc. most places will not sell to US citizen but it's good to know the pitfalls. being a part owner of a foreign corporation to name a few.
feel free to come back and ask questions. i renounced now but with the few years that I was in the system (i more or less renounced right away) i managed to learn the pitfalls which helped in this decision.