If I apply to 10 undergraduate schools what're the odds I get into AT LEAST ONE?

The OP didn’t ask about applying only to Ivies. She asked about schools with admission rates in the 5 to 20 % range. So while I agree it’s a useless question, there are plenty of schools in the 15-20% admit range which might be more focused on her ACT score or less concerned about the weaker 9th grade GPA.
Those schools would still be reaches, but definitely not impossible.