Is your question whether or not your wife will need a transit visa for the UK? The green card she holds means nothing there, but rather the passport she carries.

KL and DL both use Terminal 4, so the connection is a matter of disembarking from one flight, going through Security at T4 Flight Connections then through to Departures. She will not go landside at all at T4 so a transit visa shouldn't be necessary unless she wishes to leave the airside zone, as it is at that point she will go through passport control. It does depend on the passport your wife holds, though, so see below for the official information.

http://www.ukvisas.gov.uk/en/doineedvisa/