Hello,Hi,
This is not acceptable. The funds must be in your own account. The only acceptable joint account is one with a spouse not a parent or anyone else.
I would suggest you move the funds into your own account and accept them as a gift deed from your mother.
regards
Transferring the money without legal paper or proper proof cannot work because they have to be there for the past 6M to be above the required funds which means the direct increase in funds will be suspicious.
I would suggest to get a letter affidavit stating that you have access to this money to be used for your immigration. You can check on coc website regarding proof of funds when the money is not under your name. Hope this helps!