Would i be liable if 21 year old girl left my house drunk and got into care acident?

If she was the driver and she had had some alcohol to drink at your house you would be. Anyone leaving your place intoxicated no matter what their age is someone you are responsible for. Them being 21 or older simply means they were of the age of consent to be drinking alcohol, but it doesn't mean they were of sound mind to be driving. If they drank at your place then you are held partially responsible for their inebriated condition and anything that comes of it. That is why taverns cut off patrons and will even resort to calling them a taxi to take them home at times.