what do i do next?

to cut my story short,
my sis in law had her visa refused in aug 09 and we submitted a appeal, went to that in march 10 and had recieved a determination 3 days later saying it was allowed.
my sis in law had then received her call letter in order for her to submit passport in may 24 2010. but since then has not heard anything since. have contacted my mp he wrote 2 letters saying what is going on?
he got a reply saying we are going to conduct further enquiries. does any body know what they are doing? its unusual for them to conduct further enquiries why not issue visa when appeal is allowed. its been 5 monthe aint heard nothing can anbody shred any light on this matter please.

many thanks

it may be that they disagree with decision to overturn the initial refusal and wish to challenge the appeal decision which is their right but this is highly unusual