She (I) needs help.

My begonia was not doing so great, her leaves got crispy and dropped so I cut it and propagated, it's rooting well I guess, but what do I do with this leggy thingy I am left with? Even when it pushes new leaves, they get crispy. I even put a humidifier next to her, but no help. She sits next to a big window, but it's winter now, so it can't be a sunburn – there's no direct sun currently. Maybe a grow light burning? Any suggestions what to do with it would be much appreciated