londonandwhere, I do not understand your attitude to our MIL. You didn't find it racist at the time, but you're trying to find it racist now.
You posted :
"The reason I ask you all posting here is
I wished I hadnt experienced racism from my mil it would be extremely shocking
but if it was,
I wanted to tell my husband what his mum said was slightly racist in an unthinking way."
He was there at the time, standing right next to you. He answered her on your behalf, because you were hesitating to do so. Don't you think if it had been racist, he'd have noticed it right there and then? Instead, it made so little impression on him that he can barely remember it.
If it helps, I do not presume that people who have been resident in the UK for a few years are necessarily fluent in English. Growing up I knew many Italian-Scots. Those my age (2nd generation) were bilingual, or had English as their first language; but often their parents still struggled, despite having been in the country for decades. The Italian community was large enough that many of them rarely needed to speak English, and so were not fluent.
I think you need to reflect on why you are doing this. It is not healthy to be picking over past imagined slights (and it IS imagined) looking to start a fight.