Thanks for all the replies.
Originally Posted by Chuchinchow
If your sister (or anyone else in a similar situation, come to that) wants a definitive answer to the problem you have described I would suggest that they contact Lufthansa, Air Baltic, British Airways etc directly.
Absolutely correct, of course, but at the time I posted last night BA customer services was closed and I didn't think I'd have a chance to call during their opening hours for a few days.
As it turned out, I was able to call BA this evening: if we fax a copy of the deed poll to them they'll re-issue the ticket for a fee of £30.
I don't know how much (if anything) EasyJet will charge as I was kept on hold on a premium-rate line until I gave up (so if there are any EasyJet staff here who know the answer I'd still be grateful for a reply). Haven't had a chance to phone Lufthansa yet, and Air Baltic weren't really much help: the person I spoke to just kept repeating that we'd need to buy another ticket and I got the impression that she didn't understand that this was a change of name for a passenger, not a change of passenger. Or maybe that's the policy?
Originally Posted by Juno78
I notice, however, that the OP says "She is required to apply for a new passport in her new legal name". Is there some obligation here that hasn't been made clear or is she just mistakenly thinking that because she's changed her name she must change her passport immediately?
As I read it, there is an obligation to apply for a new passport when your name changes. The website of the UK Deed Poll Service says:
The name on your passport should always match your legal name. So if your name changes you need to get your passport reissued in your new name.
The Immigration and Passport Service website is a little less definite, saying:
You should get your passport amended if you have changed your name - whether by deed poll or through marriage or civil partnership.
I'd suggest to my sister that she keep her existing passport and travel under her married name for a while, but the risks involved in completing an ESTA and attempting to enter the US under what is effectively a false name are probably not insignificant.