Originally Posted by
JimInOhio
Doesn't UA have a semi-official flat tire rule to cover missed flights? I wouldn't automatically assume she wouldn't be accommodated.
If the BA flight is going to be late then it's likely that's known before leaving LHR in which the problem can be dealt with up front, including being put on the earlier BA flight or an AA flight to ORD.
OP said she'll have carry-on luggage only. UA is in T1.
If OP is on a single ticket, BA will rebook him. I doubt that UA would accommodate across separate tickets as that is the essence of single vs. multiple tickets. I certainly would not take that risk by bookings so close and then hoping.