I think other posters may be right about a touch of baby brain re the chip pan and I agree with the suggestions about more help and support from those who love DIL and the children.
However, I got to know a lovely Polish family very well and there were some small cultural differences which actually caused some quite big problems for them. Equally, some of our wee Scottish ways also caused confusion for them and it was only with the help of a very motherly (some would say nosey) neighbour that we all learned where boundaries lay. Language was not a problem as the Polish woman had taught English at secondary level and worked as an interpreter. She still felt very isolated at times.
It must be very difficult to be far from home with young children and not have an ear for languages. Maybe the DiL worked with other Polish people and chatted to them without having to absorb so much English. And maybe now she feels she can't go to toddler groups where she might make gaffs (I'm sure she wouldn't but she hasn't a sister or bilingual companion who could go along to reassure). She needs a friend. Possibly a quite pushy one.
One of the things which we learned on our neighbourly curve was that Easter was as big a deal to our Polish friends as Christmas is here. It was a time for family and special gifts. They gave our little GD soft toys and lovely books about ducklings and angels, all beautifully wrapped. Maybe you could find out if your DiL is missing her own family and help her out with sending something appropriate.
Loopyloo has the right idea above. If DiL is religious, could you find out when the church times are and babysit specially?
Please keep on trying to help this young mother in positive ways. Maybe you could wrap special Easter presents for the wee ones or conspire with your son to arrange an easter egg hunt just for HER. The wee Polish boy we knew (now adult) got the greatest of pleasure re-hiding his chocolate eggs for his mama to find and share. Still does.
