Could i protect flowers with a plastic bag?

ok so i am 16 but that prolly doesnt really help. well i am going to put flowers on her doorstep tomorow morning before she wakes up so when she wakes up she will find it. it will have a note with it too. well the problem is that it will probably snow tonight and so i dont want them to die before she sees them. so how do i protect them from the cold? also on christmas i will tell her i sent them. but how long can flowers like roses stand the cold? and how do i protect them from it?