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Hello. Thanks for the question.
The dose range for Benadryl is 1-2 mg per lb body weight. It can be given every 6-8 hours. You gave 12.5 mg (1 teaspoon/ 5 mL). That's 2 times the high end of the dose. The good news, is that Benadryl is very safe. Even at high doses, the most we typically see is a little GI upset and some lethargy. She'll probably just sleep it off. There is nothing to really worry about.
I hope this helps, let me know if you have any other questions.