In a word, no. Not just by erasing one name and inserting another. There are far wider/bigger (legal/practical) implications.
There are two transactions there.
1. Her transferring/releasing/selling her share to your partner and
2. the partner either assuming all her liabilities under the mortgage or you and your partner taking out an an entirely new mortgage to discharge the old mortgage.
There are stamp duty ( and possibly CGT/CAT) implications also.
If you want to post the figures ( purchase price, current outstanding mortgage, current value of the property ), whether any payment is being made for the transfer, whether your partner is a first time buyer etc.,etc, it would be easier to comment.