Hi Fiona,
just to clarify, restricted performance is in fact limp mode. It should be ok to drive but expect lower performance and hgher fuel consumption.
If you can find an alternative route avoiding the motorway, i think i would probably do that, not that it's likely to break down but if it did, at least you wouldn't be stuck on the motorway.
My thoughts are with you for your mum, i also have a (sort of) family member in hospital at the moment so i understand what you're going through, hope both your mum and car make speedy recoveries!