OP I saw your post in r/squirrels and I also live in Philadelphia. If you can get her in a cage (you can buy humane trapping cages called HavaHeart on Amazon) and take her to the Schuylkill Center Wildlife Clinic, they should be able to help!

It's about a 25 minute drive from Center City. It's kind of off the beaten path but a GPS can get you there.

This injury is a very survivable one with human assistance for a squirrel. But you need to get her there ASAP because the wound could easily get infected or become gangrenous which would likely lead to her death.