May I make a suggestion, Use your phone or a tape to record the next time she is with you . Try to be fair and just talk as you normally would do, not especially trying to get her to moan more than usual. Then later when she has gone, listen to it yourself, so that you can confirm that she is way over the top about money all the time. Then preferably with another family member arrange for her to come and have a coffee with you, and when she is settled down, bring up her attitude to money, and then play the tape to her. This way she cannot deny her behaviour and attitude, and you can lay down some rules for the future. So at this age she is not going to change much, but you can take charge of the amount of time given over to it. So for instance , you might let her start talking about money , but then say I know you want to talk about this , so I dont mind, but once we have lunch/tea/coffee, we are going to walk round the garden and dont want to talk about this any longer. If she continues past the time you say, be polite but say that you must go now. If she protests and asks why you are going you say that if you are not going to talk about anything else or be interested in anyone else then there is no point to your staying. If you can encourage other family members to do the same, you wont change her views, I think that would be unlikely, but you will have at least provided yourself with a halt to such talking, and can leave early. Alternatively , you could try , every time she speaks about the bank or the money, you interrupt with your version in your own bank, so that you cap and stop her hogging the conversation about money as soon as she begins. If after a couple of visits you find she is not responding at all, then I suggest that once she begins to talk again about such things , you quietly collect your coat and begin to leave. If she asks why you are leaving, you say that you had already said that you would not stay if she went on about money again and so you were doing as you said you would.
At least that way, you are doing your best to keep some contact, but are not letting her drag you all down and make you miserable.
Good Luck