My mom's 7 year old longhair indoor (apartment) cat (she never goes
outdoors) has a corrugated scratching post on the floor, and for the last
2 weeks she occasionally drags her rear end across the cardboard.
I've seen her do it across the carpet once, too.

I know it's sometimes an indication of tapeworms (or an impacted anal
gland).  She was just examined about a month ago, and her a stool sample
tested negative for parasites.  The vet told me that the stool sample
isn't tested for tapeworms.  We examine the stool on a regular basis to
see if there are little white rice looking things.  My mom even breaks
the stool apart to see if anything is there and it looks clean.  There's
also nothing around the hair at the anal region (other than an occasional
small thin piece that sticks to the hair).   She's active, has a nice
coast of hair, and has a good appetite.  Her main problem is that she
lost alot of her small teeth before we adopted her, and her remaining
teeth have some tartar problems.  She also sneezes on occasion (once
every few days) and we just finished giving her anti-biotics for an eye
infection.  I'm guessing that she may be allergic to the carpet dustmites

What I did find underneath her corrugated scratching board were about 8
very little, hard black dots that seemed to have two miniature white dots
on one side.  I'm assuming these were dried up dust mites, but they could
also have been dirt.

Anyone have any ideas or knowledge as to how to treat the above.   I'm
taking her back to the vet in a few weeks for a booster shot.  Comments
on boosters would also be appreciated.  It's mandatory for animals to
have rabies shots every 3 years, but I hesitate to do that since this
animal never leaves the apartment.