My 10 yo DD has recently started spitting. She does this all day, anywhere. I make her clean it up if she spits on the floor, encourage her to use a tissue or toilet. She says she has a bad taste in her mouth. Does this sound like a manifestation of anxiety disorder? Or something else? Any suggestions as to what I should do, besides buy the kid a spittoon?

I would take her straight to a doctor. I Googled "bad taste in mouth" and the first site that came up said:

The medical causes of a bad taste in mouth can include the thrush, disorders of the thalamus, Sjogren syndrome, cancer, influenza, cold, Bell's palsy, skull fracture, and viral hepatitis.

B12 deficiency, zinc deficiency, and medications such as vincristine, vinblastine, procarbazine, right fan pen, lithium, captopril, and griseofulvin can also be a cause of a bad taste.
Edit: I just realized this is a post from last month! My advice stands, though. :o