Joint mortgage - Both credit checked?

Hi,

A friend and I are thinking of buying a house together in the next year or so. I have checked my credit rating and it turns out I have a default from 2011 which I was completely unaware of! I think it may be a mistake, so I am contacting the lender to see what happened and see if I can have it removed, but this means my credit rating is poor.

Between the two of us, I have the higher salary and she has the better credit rating. If we went to a bank, would they be checking both of our credit histories or could we get away with using just hers?

Thanks in advance for any info.