Do you want your kids to be in her wedding, or not? If not, you could respond to her next hint with, "You've been hinting about this for a while, but honestly, we're just not able to accommodate the extra time and expense right now, no matter what you're thinking of" (or however you want to phrase it).
When my friend started hinting about planning her wedding, I dropped my own counter-hints about not wanting to be a bridesmaid. When the time came she still asked, but did so while acknowledging I had previously said I wasn't interested, which made it very easy to stick to that. She also had a back-up plan of me doing something else in the wedding that I agreed to.
I don't know if that would work in this situation, because here the bride has been hinting so heavily--not just about her wedding party in general but specifically about including someone from your household. "Glad my kids have never been asked to participate, we just don't have the energy for that right now" would not come across as innocent at this point.