>> reporter: ceri and rory's california home is littered with toys and medical equipment.. the rare genetic disease slowly killing the motor neurons in their daughter's spinal cord. >> you're such a brave girl. you didn't even cry when they put the iv in. >> reporter: they're now waiting to find out if the most expensive drug in the world, worth $2 million, will help save her life. >> it's a couple days after infusion, and rhys is just having a crummy day. and it just sucks. and i just feel bad that i can't help her. >> reporter: were you nervous that it might not work? >> i don't know if we were nervous that it wouldn't work. i never kind of let myself think that. >> reporter: as the couple waited to find out if zolgensma worked for rhys, ceri continued to document the highs and lows on social media. >> look at you go, rhys. >> reporter: she also relied on a facebook group for s.m.a. parents. >> my name is erin, and i'm a mother to emma. she is a 4-year-old with type 1 spinal muscular atrophy. >> my husband and i have two kids. >> our daughter hayden has spinal muscular a

i am not going to lie, cerys, i feel a bit unnatural here. i look the part...got a little echo. plays harp. like that, and back down again, then here... it�*s really messing with my eyes, how do you do this without going mad! that was the first bar of a famous welsh tune called pwt ar y bys, which is the one everyone learns first, so you are well on the way. you�*ll make a star of me yet, cerys. what a trip! wales has made me feel well and truly welcome. and that�*s what�*s really struck me at every turn during this journey — the openness of the people i�*ve met, their history and their hope for the future. next time, in the final leg of our uk series: christa is in northern ireland where she will take to the skies... try her hand at oyster shucking... and explore one of the country�*s magnificent natural wonders. incredible. legend has it that it came about because of a fight between two giants. hello again. the weekend�*s weather was always going to be dominated by showers, showers coming from big clouds like these that were spotted over the skylines of staff