well at ds's first birthday party, there was a mum there with her baby who was a couple of months old...baby falls asleep and i offer ds's bed..so she puts him in..i organise the monitor etc and mum and i walk out when she closes the door...she sits down in the living room and i went to get the handset..went to give it to her and she says "oh i just leave him (as he was crying), he'll get over it soon and go to sleep" ..so i just said "just in case..." and i turned it on and gave it to her....
not long afterwards, she got up and acted a bit more concerned about her little one... i went off to do stuff..and when she had been gone for a while, i asked her dh where she was and he said she went to hold bub til he went to sleep...
i reckon from the vibe of things and the way she looked at me that she felt a bit guilty at letting him cry, so she held him to sleep...
I reckon if i were in your situation, I would probably ask how the mum is coping...Sympathise with having a crying baby..and then ultimately offer my help "let me give you some peace and quiet"...and go get the baby and give it what it's asking for...
(all that being said and done I would have to make sure my own little one was being looked after first)

