Every time I go to buy concrete from her, she is kidnapped, again.... Like 5 times now. Even built a maximum security cell around her... Still gone. Anyone else have or solve this issue?

Lol This happened to me way too often. It's like she has a "Kidnap me!" sign on her back. She has the worst luck and needs to stay inside behind barricaded doors.

Everyone loves Conney so much they kidnap her!

It is just your bad luck I think. The whole kidnapping mission randomly attacks named NPCs in your settlements.