I have my 8 year old desylum at 8 is it ok to give her benadryl (diphenhydramine) 7 hours later??

Is it delsym (dextromethorphan)?: if it is plain delsym, no problem, but if combo like delsym nighttime or so, it might contain an antihistaminic as well, check the ingredients, and better not to combine it with benadryl (diphenhydramine) if it contains an anhistaminic, goodluck

OK: It is safe. If his symptoms don't resolve see his doctor. It sounds like he is needing a fair amount of over the counter medications. All the best.