My sister is selling car to my daughter and we can't find title. My daughter needs the car right away. Do you have any answers so she can drive it before we get the title back. Pa laws are different so I don't know?

Are you saying you can't register it?

I bought a new car and didn't get the title for 5 weeks. In the meantime I drove the car.

This is a legal question, and I've asked that it be moved.

It is registered to my sister and we want to buy it and drive it until the title comes and this is in Pa.? I am asking if we can do this without the title?

You need a tag of course. And as you know, PA farms out issuance of tags to certain notaries, title service companies, and messenger companies. I suggest that you contact one of them for guidance on the best way to handle this. They may be able to issue you a temp. tag based on their personally observing the serial number of the vehicle from the tag on the dash.

This is one of the large service reps in my area with other offices in central PA (not a friend or relative of mine by the way). Call them and they will know how to get you on the road and give you guidance (or use one you know of in your area):
Sollenberger's Messenger Service Inc.

This is access to the PennDOT form for replacing a title:
Pennsylvania - Replacing a Lost Title - How To Get a Duplicate PA Title at DMV.org: The DMV Made Simple

Will sister just leave it in her name and let daughter drive it, till she gets the title.

You can not change ownership and register it without the title