Another newbie here, popping over from Mumsnet which is a great place to read up on DIL's bugbears (I've learned a lot!)
In answer to how not to offend future DIL, I reckon being considerate, uncritical, caring and fair,not giving advice unless asked for and following any rules for looking after DGC to the letter, no matter how ridiculous you might think they are, are good starting points. If DIL wants DGC patted exactly 4 times on the back after 3 mouthfuls of puree and then massaged with goose fat for 32 minutes, bite your lip and crack on. And remembering that new parents are vulnerable and often unsure of themselves and might need TLC in the first few months while they get to grips with thing. It's flipping difficult to navigate this whole MIL thing at times I've discovered.
Am looking forward to checking out some of the threads on here.