Some of Riser's friends come over to watch a rating game, with Rias naturally providing snacks, beer, and some further entertainment to enjoy themselves. Just what she needed to complete the next step in executing her plans against her husband.
At least when it came to dealing with Riser's folks, Rias was able to get them on her side quite easily. The fact her in-laws also suspected their son to be up to no good and dealing with shady investments helped her out quite a bit.