I've never seen an anemone extrude itself that much, but it's likely trying to rid itself of the silverside.
If you have a QT tank, I would get it in there (with freshly made water) ASAP. Depending on how it responds, I'd do a daily 100% water change to remove the ruined water, and so it can take in completely clean water. Hopefully it responds positively and recovers. It might be worth it to consider antibiotic treatment, but you should know within a day if it'll make it or not.
Something that should be a hard and fast rule with any new anemone: Don't feed it until it's completely settled into the tank, wait at least a week if not longer. Anemones are probably some of the most sensitive creatures to adapt to a completely new environment, and the stress they undergo the first few weeks/months settling in is enough to kill them. Feeding too early only adds to the stress and can hasten their demise.
I'd also avoid feeling silversides altogether, they can go bad quickly. There are a few anemones on here who've been lost to a spoiled silverside.
Crossing my fingers for your friend and the anemone, good luck!