My daughter has a rash all over the top of her body which looks like an allergic reaction but dr said it's roseola but she didn't have high fevers

Possible. Sometimes roseola rash can look like macular patches and spots and can be mistaken for allergies. High fever is common but not always seen. If it disappears in 2-3 days with no anti-histaminic medications, it is likely to be roseola. Above is a link of such a rash.