Does the orgasmic meditation group my clients belong to pose a danger in attracting spirit attachments? If so, would requesting safety by the divine realm before each session prevent this?

Indeed, this is a risk factor, and as you have seen intuitively, is the reason that you found your recent client to be re-infested. This was impulsed to you by your higher self to repeat her work, and thinking this had been arranged, when in fact she had been done through a gifted session previously, and would ordinarily not have been addressed again so soon by you. So this was a way to alert you to this phenomenon and this potential vulnerability both. The vulnerability from having a sexual encounter is not a risk per se, it is doing so in reaching out for a higher awareness at the same time. The reaching out without protections in place will always invite many beings to come to the party, so to speak, and in a sense whoever gets there first and does a handshake will be invited in. This is what has befallen your client. So to ask for protection would be a good idea and would be effective in safeguarding such an undertaking. This must be the intention of both parties involved in a session involving a couple.