I can't believe other mothers judge others for whether they work, stay at home or what. We should all be supportive of each others decisions, especially being your own sister Tracey. Its a personal choice and these days finance also plays a part, not everyone can afford to be a SAHM.
At the moment I'm on mat leave but plan to return part time to work just so I can get that balance, everyone just needs to do whats right in their situation and respect their decisions.
If your sister is so broke and bored why doesn't she go look for some work? I think she just makes all these comments about you because she is jealous.