My daughter no longer wants to sleep on her own

[HomeintheSun]

In brief, my DH is away for 4 months so the DC and I went to stay with family for 6 weeks, in this time the DC (DS 4.9 years and DD 22months) slept in the same room and DD loved this, we came back to our house on Wednesday and ever since getting back she has not wanted to settle in her own room and for the last few nights it has been a battle.
Moving her into DSs room is not a possiblity, as if he falls asleep first she goes and punches him in the head.
I did have a bit of a problem after spending 2 weeks away over Easter, again my DH was away then it was for 5 weeks, but then is only took 2 or 3 days to get back into her routine.
My sister suggested getting a cd player for her room and playing soothing cds but has anyone else got any experience of this with their child and if so how did you get past it??
I need some help now because I cant have the same battle every night for the next 11 weeks.