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Lavenders are very even in color(or shaded if the bird has both gold and black pigments). No dark splotches, laces or having the tail/hackle/saddles distinctly darker than the body(more noticeable on adult blue roosters). One of the common names for solid lavender birds is "self blue" which hints at the even-ness of the grey shade on lavenders.
Blue on other hand is extremely variable, can be really light(some even look so light/even they look lavender-ish) all way to so dark they look visually black(and surprise the owner by producing more obviously shaded blue chicks...). They also can be bred to have a laced look to their feathers(light blue feathers with black edges)- afaik, not possible with lavenders. Very common for roosters to have hackles and saddles a couple shades darker than their body. Hens with heads and tails darker than on body is also common but there are plenty with the same shade throughout.
Your Arianne has dark splotches which rules out any chance of it being lavender.
One other hint of blue vs lavender is if the bird has gold pigments anywhere on it, it will be diluted to a straw/blond color while on most blues, the golds will be either normal or almost normal. There are unrelated genes that can lighten the gold, if these are on a blue/gold bird, they can look almost lavenderish, those are relatively uncommon & usually don't have a strongly "pastel" look(porcelains are a great example of how lavender works on black and gold pigments).