Hi welcome to HCM... I can understand your concern.... Let me explain you benadryl contain first generation antihistaminic drug like diphenhydramine ....So it has having side effect of sedation.... So your child felling sleepiness , no worry for that .... At home based treatment keep the area clean with water and soap.... Cold compress can be applied for reducing pain and swelling .... Topical steroid cream or calamine lotion can be applied .... If your niece having .... /Diarrhea / laryngeal edema leading dyspnea / large swelling at bitten area than consult to er. Hope your concern solved .. Advise : Nearby doctor consultation for examination of bitten area For further query you can use premium facility available in this site Tale care