ORD is no difference than SFO or LAX regarding INT-DOM.

Either you can get out of the terminal (T1) after you arrive, take the airtrain that is outside security and wait for her at the arrivals hall at T5 that is where all international flights (except canada) will be arriving.

Or either wait at the entrance of one of the RCC at T1. LAS flights will likely depart at B gates. Therefore either meet at the RCC at B6 or B16 depends on where your LAS flight departs. You can check flight gates 24 hours before departure on the UA site to see where it is going to leave from unless they decide to change the gate last minute.