elizwlsn, was the lavender egg you hatched expected to be a lavender bird? Was the mating from a lavender to a lavender, or could it have been lavender to a black carrying a lavender gene or lavender to black non lavender? If so the lavender egg could have hatched to be a black bird carrying a lavender gene.
If the hatched lavender egg was certainly going to be a lavender coloured bird, then the likelihood is that she is the bird on the left. I have a lavender bird with a darker head for some reason thatI do not know & it is not from the same lines. I have not seen lavenders with black spots. There was a lavender with black fathers recently but your bird does not look the same. Perhaps the black will moult out.
You will be able to tell for certain if she is lavender by looking at the feather shafts, an andalusian blue can have darker shafts on both sides of the feather. Also quite often lavender birds has a sort of silver sheen.