Serina would watch their battle though an upload link between all their Rotom phones, a small ding would sound on all their phones to tell them that Selina was there if they needed advice or how many turns they had left before they were blown out the den. Since only 4 people could tackle these battles, Selina was quite happy to watch her friends battle the giant pokemon. 
Though she quickly spoke up to Liam "By the way, even if you fail this capture, you're still rewarded with a bunch of random goodies from TR's to Exp candies. You'll have to pray though as you'll only get one chance to capture this pokemon before it flees"