your friend can't be certain of the actual filler that was used. Whether collagen, or any other filler, substantial volume would be needed to create a visible improvement in an area that large. Once such sufficient volume of filler is inserted, there is a concern of migration, nodule formation, scar formation, necrosis (death) of the skin and ulceration (open wounds). Infection has occurred from improper technique and the use of non-sterile substances. Immune reactions have occurred from the use of products having adulterants (additives) or the product itself (e.g. paraffin waxes). Silicone reactions have been noted as much as 25 years after a procedure was done, so although your friend is OK now, she might not be "out of the woods" for many years depending on what substance was injected into her.
Remember, you are doing a cosmetic procedure to enhance the aesthetic nature of your physique and if a complication arises, even if it is of low probability, the aesthetic outcome could be disfiguring and permanent. If a complication occurs when you are treated out of the U.S., it is possible that your medical insurance would not cover the cost of the treatment of complications whether overseas or here in the U. S.