We Are Giving Our 11 Year Old Daughter Maintenance Allergy

We are giving our 11 year old daughter maintenance allergy shots at home. Tonight's shot, done by my husband, was done lower on her arm than normal. It's now swollen but not red and no more itchy than what the clinic said was normal. Is it possible that it just went into some muscle? Husband thinks it's fluid or something but what would it be?