I have done interlining many times on international flights. In 2007 I flew from SFO-FRA-TLV. The SFO flight was operated by United and the FRA-TLV was operated by Lufthansa. The agent at SFO checked my bags all the way to TLV with no issues. I was told to go directly to the gate and that I would get another boarding pass from Lufthansa but that I was checked in all the way through.

Last summer I flew from SJC-ATL-CDG-MXP-TLV. The SJC-CDG via ATL was operated by Delta and the CDG-MXP-TLV was operated by Air France and Alitalia. All my bags were there waiting for me at TLV.

I had to go to the transit counter at CDG to get my boarding passes.

So I would recommend that you arrive at the airport at your departure point at least 2-2.5 hours before departure even if your flight is a domestic sector as the agent needs to check your documents and check your bags in. Make sure your wife tells the agent that she wants her bags checked all the way through and make sure your wife checks her baggage tag and receipt before her bags are put on the belt.

Your wife needs to keep her bag tag with her and it will be stapled to her ticket jacket.

In most cases she can go directly to the gate but make sure she cehcks in with the agent to get her boarding pass on Thai Airways ticket stock and confirm her seat. There is no reason to go to the ticket counter as United will give her boarding passes all the way through but sometimes gate agents will want to reprint the boarding pass for some reason.

I hope this helps. Hope she has a safe trip.