It will almost certainly be classed as savings.
On Pension Credit you are allowed £10000 savings without it affecting the amount of the credit paid, & you are generally allowed to use savings to pay debts which are due without penalty.
The £62 p mth will be taken into account as income at present, & so reduce the Pension Credit amount. You need to confirm whether the amount of the credit would be increased if your wife takes the lump sum.
Contact your local CAB for confirmation, & for any other advice.