My daughter is almost 8 months and diagnosed with moderate to severe sleep apnea. she is on prevacid (lansoprazole) for acid reflux is this the cause of the apnea?

Very unusual: If i understand this correctly your eight month old child has significant sleep apnea. This is very unusual but can sometimes occur in the face of enlarged adenoids and tonsils. Reflux can always make things worse, but reflux by itself usually will not cause such significant apnea. If you have not already taken your child to a pediatric ENT doctor you should.