There is no workaround on the 12 week release date other than it is slightly extended at the moment with booking available up until 31 May.
I am sure the workarounds you mention are related to using 3rd party websites. Do not do that, they have no privileged access, all they are doing is taking your money now on the promise of securing tickets when they are released.
That is just foolhardy. There have been long periods of time this winter when the sleeper has not run due to major engineering works in Devon and Cornwall.
Wait, like everyone else does, until tickets are released.
Timetables are not released to GWR by Network Rail until that 12 week deadline- sometimes less. GWR will not take bookings on day or night trains until that confirmation is through.
When released tickets can be purchased online, but only through the GWR website or app. The app is only available in the UK and is horribly glitchy, but the website works anywhere. Only recently an Italian lady on this forum purchased on the GWR website using an Italian credit card, so you are being given wrong information.
Your implication that getting a local to purchase the tickets for you could go wrong is unfortunate.
It is not how you get favours done for you.
I do a lot of genealogical work for overseas clients. I can't tell you how often I have been short changed by such clients paying me net of the PayPal charges, or deciding to otherwise short change me. So much so that my hourly rates now assume that everyone overseas is going to avoid paying the full sum, the rates have accordingly been lifted and I now insist on full advance payment. I utterly hate having to assume that everyone is a criminal.
If your daughter is in London what is to stop her going to Paddington ticket office on or after the date of release, and paying in cash- physical bank notes? She must be able to withdraw cash from an ATM in London.