Can you think of anything that may be different? Are there other changes going on or could she be teething or unwell?
As to whether it's a bad habit - that's a personal opinion.
On this site, among those following BW, most would feel it's unwise to let this particular habit form. She's using you as a comfort and at night is not learning how to sleep independently. In the long-term it could result in some difficult times. If you're not comfortable with it - I would nip it in the bud and try and break the nursing=comfort association.
On other websites - like mothering.com or breastfeeding.com for example - where 'attachment parenting' is the norm you'd be describing a common situation. Mothers there regularly co-sleep and nurse all night and wait for their babies to 'grow into' sleeping more independently. (could happen 3/4 years +) Tracy would probably say don't do it unless you're prepared for it to be permanent.
If you are not happy with it (and I'm guessing you're not?) you could have a look at the props board or this sticky to start.
https://babywhispererforums.com/index.php?topic=52857.0