I think she’s being taken advantage of.

Ask to speak with her GP stating your concerns, they will know if they are vulnerable & easy to manipulate, sadly one of the hardest parts of the condition to see, if they have concerns ask for a referral to the consultant fora further diagnosis to assess capacity, if that isn't working go to OPG & inform them of your concerns, document every conversation for your records. The banks also have a duty of care to protect your mothers finances , she will be asked if she is withdrawing money what she needs it for & will be invited to do a bank transfer.