Cutting back teeth at four months! Is this normal?

[fizzbuzz]

Have just discovered dd who is 4 1/2 months old is cutting back teeth! Is this normal? She has no others at all, but definitely has 2 top back molars. How weird is this?
Ds cut one "fang" at the side of his mouth before any others, again at the top.
I thought it was bottom 2 front teeth that came in first. Any advice?

Usually the first teeth through are the 2 front lower central incisors, then the ones either side of them, followed by the same pattern at the top. Next are the first molars then canines then back molars. It is unusual to have a different order but not unheard of. If you are concerned take her to the dentist to check it over.