From Colette's blog some clarification as to why Katie was allowed to play here
"Swan, who is from Great Britain, just received clearance to play the Easter Bowl last week, after her father was transferred from London to Wichita, Kansas.
"I moved to the United States just over a year ago, and we've been applying for a green card for a while," said Swan, 15. "To play this tournament we needed the receipt to show we are applying for one, and it came in just a week before this tournament. So it's pretty lucky, and I'm really happy that it came."
Does that imply she will swap to representing the US?
To become a US citizen I believe you need to be a permanent resident for 5 years, so even if she was considering that route, and that must be highly doubtful, it'll be a long while before it could happen.
Hopefully nothing to particularly worry about, going forward, re the trainer callout.
Colette's blog helps to clarify:
"After falling behind 2-0 in the first set, Bellis won six of the next seven games to take the set, and continued to dictate points with her forehand in the second set, while Swan's serve began to become less effective. Swan called for a trainer at the end of the first set, with her shins the source of the discomfort.
"Yesterday both my shins started to hurt. I think the tissue is rubbing on the bone," said Swan, a 15-year-old from Bristol, England, whose family now lives in Wichita, Kansas. "But it will be okay soon."
Swan had nothing but praise for Bellis.
"She's such a great player," Swan said. "It's great to play against someone like that, so I know the level I need to get to. She's just looking always to dominate, and has a great forehand. She's just an amazing player."