The cat should be secluded in a room of her own with a bed, litter, food,
and water. Your friend can sit with her, etc. She may or may not be able to
integrate her into her home with the rest of the cats. A move for a 10 year
old cat is traumatic. If the pooping and urinating inappropriately continue,
she should be seen by a vet to rule out a medical problem.
Gail

Are you sure its 6 months... about 4-5months ago I read that it was changed
to 1 month with proper vaccinations, certificates, etc.

Chris!  Also try sending your friend an article of clothing with your
smell on it (maybe a t-shirt you've slept in).  When trying to
integrate a cat into a new household, it's always helpful for the new
cat to have familiar smells around.  And I completely agree that your
cat needs to have a "private place" for at least a little while.  Your
friend can let your cat and her other two slowly get used to each
other's smells in the house - they can sniff each other under the door
and on her clothes.   She can also try giving your cat a few toys -
let your cat play with them for a few days, then start putting one or
two out with the new cats, at the same time putting one or two of the
existing cats' toys in with your cat.  Your cat should also
(obviously) have her own litter box at the beginning.  Like the toys
idea, your friend can start putting little bits of used litter in each
other's boxes.  The pooping and peeing are definitely signs of a very
unhappy kitty!    I hope this helps you!