Translation:Take your apple from her and give her her banana.
It's because of Schwa deletion where the implicit vowel is sometimes deleted in Hindi.
This is the same reason अपना is pronounced 'apna' instead of 'apana' and उसका is pronounced 'uska' instead of 'usaka'.
But just because उससे is pronounced 'usse' does not make it उस्से. The pronunciation of उससे can be broken down as 'us-se' while उस्से would have been 'u-sse'
I have a brain-twisting question about this already brain-twisting sentence: do उससे, उसे and उसका refer to the same person or to two (or even three) different people?
Let's assume there may be 3 people A, B and C besides you and the person you're talking to. Can this sentence mean "take apple from A and give A their own (A's) banana"? Or "take apple from A and give A B's banana"? Or "take apple from A and give B A's banana"? Or "take apple from A and give B their own (B's) banana"? Or "take apple from A and give B C's banana"? Or any of those depending on context?
PS: Sorry for the headache :-p
'..give [to] her her [own] banana'
Modern English has very few case variations, so the two 'her's here have different grammar (as seen by the different words used for each in Hindi - उसे & उसका) but the word is nevertheless the same.
It may help to realise you could also translate it as 'give him his banana', 'give him her banana', or 'give her his banana'.