I don't have any experience in this but I'm impressed with the combination you two have already come up with.
Sounds like you've laid some sensible groundwork already...This Friday no need to go beyond this event if you can avoid it.
Proceed with the funeral without being to explicit until you show her the hamster...Is there a more benign way to introduce physical death?
You will have her attention but it will be focussed on the hamster rather than you or her mother....an opportunity to reinforce what ideas you choose...no need discuss people...use the example of this pet.
Eat, watch the movie when the mother dies make the connection to the hamster...keep the focus to allow the two things to connect....let it go and finish the movie (they're all good enough to regather her attention).
After the movie she'll probably come up with some questions...steer her back to the mother then your mother.....let that sink in...
"Right!...time for bed, young lady".....use your best magic keep her distracted and stay with her till she sleeps...
...Sigh in wonder, silently thank the hampster for it's contribution & go to bed happy..
In perfect world you could pull this off!.......good skills, bro's!