Parent of my former troop wants to transfer to mine

Last year I left my troop as co-leader and started new one. It was caused by a rift between my former co-leaders and I. Since then my troop has been doing great - we’ve been very active and were featured twice on our local community social media for our volunteer work and projects. This has garnered some attention.

So, of course I’ve been quietly approached by a mom from my former troop asking to be transferred to mine, however part of the deal when I started a new troop by Council is that I’m not allowed to recruit any scouts/parents from my former one. How do I diplomatically explain this complicated situation to that mom? I can’t say that my troop is full because we have 6 girls total. Thanks.