I'd try Camp Tonkawa in Collinsville, TX. My kids haven't been there yet, but I met the owner and her 2 sons at a Summer Fun Showcase and was very impressed with her AND her sons. The camp is only about an hour north of us, and they do a lot of "nature" kind of stuff.
The rates look reasonable, but the weeklong camp is for 9 year olds and up (I'm not sure if you can talk her into letting your 8 year old attend. They have 3 day camps for younger kids. Pricing is online as well ($360 for 5-day; $195 for 3-day). Sounds pretty reasonable, but I haven't researched others to know.
Good luck!