they ususally wouldnt bother
i know a few people who forgot and woman in teh village did this week (father inlaw is doing her mot)
they will report you for it but then you go get an mot done and tell them and it wont go any further
they wont take you to court for it if you are a stand up person and you got it sorted asap

i got done once and got a £20 fine via court, and no costs and costs would have been £45 lol cheaper than the mot itself thats was and i never did mot it

get it booked in where she is but if she gets pulled and say 'oh yeah im sorting it next week' expect to get bent over as its different to not knowing
and its rare (ive never seen it myself) to have insurace based on an mot, roadworthyness yes not mot (here comes the arguement )