Should i dilute invermticin for my 109 gram guinea pig? if so w/ what?

i just order ivermectin for my guinea pig, whose 109 grams. im going to treat her for mites as shes been biting and scratching herself somethin awful with white dandroffy stuff at ends of fur(non moving). should i dilute it? if so with what? in guinea lynx it says to use .5ml of it. she isnt losing hair (ther than normal sheddi,g) her eatting habits are normal (drinking a little more but its been very hot here and she onlu drinks more when uts hot out(. she is nore skidish and scared to be picked up, but has a couple o scabs rom scratching/bitting