My sister-in-law plays the same way. She calls raises with anything and usually gets lucky on the river. I have sworn off going all-in against her unless I have the absolute nuts. You see, she doesn't have a clue about the odds. If I bet the size of the pot she will call, if I bet the minimum she will call that too. There can be 4 cards to the flush on the turn and she will still call with just a pair. I just bet the minimum amount if I catch something and check her down if she calls it. I chip away at her stack like this until she is no longer a threat to me. It takes a while but I would rather win several small pots than lose one big one to an underdog on the river.

I would also suggest playing her heads-up at home to spot tells in her game.

PipeLN