It's a bit early to worry about it going bust - the intervention by the Bank of England is intended to prevent that; Northern has a sound loan book, apparantly.
However, I believe that there is a finanacial services compensation scheme that will pay. The maximum levels of compensation are: Deposits: �31,700 per person (100% of the first �2,000 and 90% of the next �33,000). So she might get that maximum amount but not for each acount/bond.
Full/better details can be found at:
http://www.fscs.org.uk