At the doses that we need, have her take it with food. The little bit that the food interferes with absorption won't make a difference because we take such large doses. It's not likely a herx of any type, but just irritation to the stomach from larger doses of the Doxy.
As for her dose of Doxy, the doctor is correct. ILADS recommendations:
"For children 8 years and older, doxycycline is an additional option. Doxycycline is dosed at 4 mg/kg/day in two divided doses, with a maximal daily dose of 200 mg. Higher daily doses of the individual agents may be appropriate in adolescents."
www.tandfonline.com/doi/full/10.1586/14787210.2014.940900about
half way down the page, under Recommendation 2B.
68 lbs = 30 kg
@ 4 mg/ kg that's 120 and then it says in two divided doses - so that's 60 mgs twice a day.