Sorry to be so late responding. I didn't see your post until today. If you want to restrict your plants to natives only, then I would suggest that you avoid both the Shasta daisy and the oxeye daisy. Neither is native to North America, and in some areas the oxeye is considered to be an invasive pest. The Shasta daisy was developed from the oxeye daisy, so it isn't a native plant either.
I haven't had the pleasure of meeting your MIL, so I wouldn't know whether or not her horns can be seen. Hmmm ... I'll have to check my own in the mirror! Wouldn't want them to show when my DIL comes to visit this summer!