Disabled Blue Badge

My mother had a Disabled Blue Badge in Spain. She has had to move back to UK and I wanted some advice as to whether she is able to continue using her Spanish Blue Badge in the UK or would she need to apply for a new British one

Strictly speaking as a visitor yes, as a resident no, but how it's dealt with may well vary from place to place.
Cornwall for instance requires you to register your EU badge to avoid getting a fine.

https://www.cornwall.gov.uk/transport-parking-and-streets/parking/disabled-parking/disabled-parking-non-uk-blue-badges/

Given that disabled parking restrictions are fairly rigidly enforced in UK, and rightly so, I would expect parking in a disabled space in a UK regged car displaying a Spanish badge could result in some awkward questioning. As per the basic rules the badge holder of course should be driving the vehicle or at least in it.

If you are entitled to a UK badge then get one and be covered properly.