If your friend wants 8 jets at 15gpm she will need at a minimum 3" suction and 3" return to to feed these jets. To install the plumbing they need to core drill thru the spa wall to install the plumbing. Use a Waterway Plastics Poly Gunite jet body, with this you will have a 2 1/2" pipe coming thru the spa wall. The jets need to be plumbed in a loop to get equal flow.