When my grandchildren tire of doing their spellings, reading, etc., I stop. Quite often they initiate things - nan can we read a book, do a crossword, do the adjective game, etc. There is, in my opinion, no point in forcing a child to learn. It will just put them off learning.
I would do, as others have suggested, work with her and do my best to make it fun (though from what has been said it doesn't sound like much fun). I think an hour is too long. I'm fairly sure that in school children are not expected to have that degree of concentration and commitment, without any light relief, for a whole hour.