Thank you David. I must admit I didn't notice it was there for the last name too.
Would it be appropriate to also ask her to change the first name? Anonymous seems to indicate the named person's intent to remain private (and I believe it is automatically used for those who choose not to have public profiles, even though they do put their real name on their private profile). "Unknown" seems like a more accurate choice for the first name as well as the last. At this point, she may end up as Anonymous Unknown, which is still misleading IMHO.
I'd appreciate the feedback to help me better understand the ways of Wikitree. Thanks!