Here's the problem I see with her staying overseas after reaching 1500TT if her goal is to fly for a U.S. major -
Commuting from the U.K. to the U.S. for 15-18 months within no online passes?
Does her schedule have that sort of space? Like 6/6, 7/7, 14/14?
With 2500TT she will have zero U.S. flying experience, zero U.S. experience, and zero U.S. training and might be a long way from getting PIC time.
Does her British degree meet the education standards the U.S. airlines require? IDK.
She has a competitive advantage by being female. But I doubt they'll lower their minimums. Instead perhaps she'll get considered once she reaches the minimums vs. having to target achieving the average resume.
If her degree doesn't qualify for the four yr degree requirement she can go to one of AA wholly owned regional carriers. That's about a six year flow to AA.
If her degree isn't reconginzed her experience and British education credits might allow her to get s four year degree online in two to three years. If she came here next fall in three years she could have a four yr online degree, if her British degree isn't accepted, and about four thousand hours TT. By then, at most regionals, she'd probably have upgraded. With that TT, a left seat command on her resume including five hundred hrs TPIC, at tleast two types ratings, over two thousand hours U.S. experience, IMO she'd be very competitive. I just don't see how staying at her European job increases her odds. It's just more and more of doing the same flying, and outside of the U.S. with no U.S. experience.
Airline Pilot Central is where I found those resumes. I don't recall seeing any foreign pilot, with no U.S. experience, especially 121 experience, getting hired by a U.S. major. It might have happened but it's a low probability path especially for a non competitive, or barely competitive, resume.
The U.S. airlines value command experience. Even just passing the training. So for many young guys the decision is do they stay for a regional upgrade, and get one thousand hours TPIC, or do they go to an LCC and hope that experience triggers interest from a major airline. It's hotly debated but most airlines aren't saying what their key requirements are but DL has said to be highly competitive you need one thousand hrs TPIC.