Hope I can explain this clearly and concisely.
SIL is about to embark on a very large payment plan. No worries there - she has money but it's tied up with no instant access or easy way to get a statement.
What she wants to do is ask MIL to transfer £15k into her bank account and get a statement to the company organising the payment plan to prove she has funds to support her lifestyle. Then she transfers the money back to MIL.
Again there is no issue with money - MIL has it as a safety net and SIL wouldn't try to keep it or anything, but I'm concerned about the Money Laundering regs. We had to prove where our deposit for the house came from. Will MIL have any issues if she agrees to this?