US Greencard holder traveling through UK to Europe

[sumdesi 3]

Hi,

My wife is an Indian national with an Indian passport, who currently resides in the USA with a green card.  She will be flying through London airport on her way to Paris in a few months.  She booked her flight from USA to London separately from her flight from London to Paris.  Therefore, she will be switching planes and moving her baggage from the first airline to a different airline in London.  Her departure flight from London is on the same day and same airport as the arrival flight.

 

The UK transit visa website states that you need Visitor in Transit visa if you will be going through border control, which I believe will be the case since she will be grabbing her bags from the first airline and checking them into the second airline in London Heathrow.  However, it also states that you may use the transit without visa option if you are traveling to or from USA, onward outside of UK within 24 hours, with the departure flight from London being on the same day as the arrival flight into London.

 

So we are confused whether she will need a visitor in transit visa or not.  Anyone else have a clear idea of how UK transit visa process works, and which of the above rules supersedes the other?