Personally, I wouldn't be comfortable making that kind of decision about a character I didn't create, especially one that's used communally. I'd much prefer it to be left up to interpretation by anyone who chooses to write her.

That said, we can make some reasonable deductions based on TOS, which would be the only definitive source. I'm not aware of any clear statement of her height—however, we know Acacia is "fairly tall" and Jay is even taller (TOS 10). It probably would have been pointed out in the unlikely event that Lux were also taller than Acacia, and it also probably would have been pointed out if she were significantly shorter, so I think we can safely assume she's somewhere between average and "fairly tall."

So, what's average? Google tells me the average height for a modern woman over 20 years old is about 5'4" (64 in or 162.56 cm).

What's "fairly tall"? I'unno, 5'9" (69 in/175.26 cm), maybe? 6 feet (72 in/182.88 cm) would be quite remarkable, so that's my maximum guess for Jay's height; Acacia has to be less than that while still being enough above average to stand out.

Split the difference between 5'4" and 5'9", and I'd guess that Lux is about 5'7" (67 in/170.18 cm). Taller than Momoka? Yes. Maybe. But probably not by much.

~Neshomeh is 5'5" and feels pretty normal.