Spoiler:
If you look at the image of Lusamine and flip it, you can practically see the same posture from UB-02 Beauty and herself. The fact that Lillie resembles UB-01 would support the whole Ultra Beasts mimicking humans situation. At least for some of the characters we've seen so far.
The posture is there, yeah, but nothing else looks like her. The hair is completely wrong and I'd argue that's the most defining characteristic Lusamine has.
You also run into the question: Lusamine will almost certainly be an important character, in which case, why is only one form of UB-02 based on her--and a version-exclusive form, at that? Similarly, who would the other form of UB-02 be based on? No one we've seen looks even remotely close. If one form of UB-02 is based on an important character, it would stand to reason that the other form is, too.