I think Rose has the final in the bag if she gets through to the final. The maths and the quality of the four remaining contestants means that anyone could go out next week, even the couple with the highest viewer vote, if the ranking goes against them and they end up in the DO against a superlative dance. They're so evenly matched that any of the 24 possible rankings (not including ties) is probably equally likely.
We could plausibly end up with a ranking of
AJ 40 +39
JJ 39+39
Rhys 40+37
Rose 38+38
Which would probably land Rose and Rhys in the DO and Rose out. Not very likely of course, because I think all the other 23 permutations would probably see her safe, but far from impossible.