It still seems unfair, because someone with no ticket is paying less than someone with a railcard discounted ticket and no railcard, and potentially charged a fare that is not the appropriate fare for the time of travel (e.g. Anytime when an Off Peak is valid). I don't consider £130 to be the 'correct' fare from MAN to EUS, because I would
never consider paying it. I'd even get Megabus to avoid paying that, and that's coming from someone who hates coach travel.
I believe that, the degree to which it can be considered 'unfair' depends on the circumstances (of course it is subjective). It may also make a significant difference if it was an outward/single or return portion. The price of the ticket held and the price of the ticket purchased would have a huge impact.
e.g. York - Sheffield passenger on a YNG SOR (£12.40), on an outward portion, told has to purchase new ticket, so pays £18.80, that isn't bad at all for the distance! They then use their new £18.80 SOR, and then 5 days later, they can use their original SOR when they have found their railcard for another journey. Total loss = £6.40. Sounds fair!
e.g. York - Retford passenger on a YNG CDR (£9.70), on outward portion, told has to purchase new ticket, so asked for £38.60 (it's cheaper to buy further OR split, but they
won't be
offered that...), they can't then use their unused £9.70 ticket as it expires that day. They can't get a refund as it's under £10. Total loss = £38.60. That's quite a lot of money for a journey of comparable distance than the Sheffield one. Sounds less fair than the previous example!
How 'fair' the OPs situation was depends on:
Where was the journey from/to?
Exactly what ticket(s) were held & what price?
Exactly what ticket(s) were issued & what price?
To be honest, it's a lottery...
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In the first example, the passenger can get 2 journeys for £31.20, for journeys that would normally cost them £12.40 per journey (£24.80) so have lost out on £6.40,
In the second example, the passenger gets 1 journey for £48.30 for a journey that would normally cost them £9.70 so have lost out on £38.60.
The distance is comparable.
The 1st example assumes that the passenger is able to, and wishes to, make the journey again within the time window that the outward portion of their (unused) SOR is valid for.
I'm unsure that the system can be considered 'fair', unless a lottery is considered 'fair'

But the OP's daughter may have been treated fairly - I cannot say without the facts requested above

Even then, it'll be subjective!