But you are assuming RG had obvious reasons for wanting a large sum of money quickly and AK and RS didn't. There are other possibilities IMO.
Could RS's allowance/account have been low?
Could they have been trying to make a drug deal?
Could AK have taken the money, and RS knew nothing about it?
Could AK have taken the money for a fast deal, planning to put it back asap?
Maybe she couldn't get to the ATM quickly enough or didn't want to make another large withdrawal. If she/they were already plastered, her/their decision making might not have been as sharp as usual.
Could AK have taken the money as a prank/joke... never meaning to keep it?
Could AK have taken the money only as part of the staging... to make it look as if a thief had broken in and taken it?
Etc...