It was odd that you wouldn't request a stinky bin be removed from a space where you were working (doing someone a favor) if the smell was so bad it made you gag. What would've made sense would be to have requested the bin be moved or to have moved it yourself.
Ignorant? Not sure who you are asking that question about. Ignorant is basically 'uneducated' so I don't see where that would apply here. It was thoughtless of the woman not to have removed the bin, but then she's likely nose-blind to the smell anyway so is no longer aware of how offensive it may be to someone who isn't exposed to it daily. Maybe in that way she was 'ignorant' of how the smell might affect someone who wasn't frequently exposed to it.
Your wife had no right to be offended that you don't want to return to smelly-house to do favors for her friend. If she was a good friend, she'd actually give the other lady some advice on how to reduce that odor or to just remove the smelly diapers from the home on a regular basis (or buy a containment system that holds the scent in, as well as the dirty diaper).
EDIT: You commented "My wife's is very sensitive to small little things, so as much as I wanted to remove it, she would have even embarrassed " to another respondent, but your wife's embarrassment is HER issue. If you are going to make it your issue as well, then you lose the right to be upset about the smell. You chose not to take action for your own comfort, because it might have upset her (and she wasn't even present at the time)...but she got 'offended' anyway because you commented on the stench. You were in a lose/lose situation, so might as well have made yourself more comfortable at the time.