So, while I'm not discounting the lassie perhaps being an attention seeking, mentally unstable fecker, could be there is another angle to this. There's this thing where people want to be disabled, think body dysphoria, but instead of thinking you're in the wrong body, you've got too many limbs or some whacky shit like that. I'm not sure the pain she'd be going through with attacking the legs, slashing and cutting herself would payout in attention unless there was some sort of end goal here, to make it all worth while. Could be the self inflicting of wounds might stop after the legs get/got the lop due to her being in 'her' body and getting the attention an actual disabled bastard would get.
Could very well being viewing this too deeply, much like how we've seen the inside of her leg, deep, but crazy does come in many different flavours and colours.