No, but she is a bad babysitter for Bart. I will list the reasons.
1. He is her older brother, and siblings, particularly OLDER siblings, will never treat each other with the kind of respect due a caretaker or someone who is in loco parentis.
2. Bart is naturally a bit of a hellion, so he needs someone who can physically overpower him if need be. Lisa is a girl and two years younger than him, so she can't do it.
3. Lisa's ego is involved, and that clouds her judgement. If it was some other kid, and not her brother, she would probably display better decision making capabilities and perhaps de-escalate the situation. But Bart has a talent for getting under people's skin.
