Four issues here
1) Problem calves and feet
2) Poverty spec budgets – and it isn’t the cheap time of year for gear
3) Risk of rocking up to a hire shop in resort and finding what’s left
4) ? being new to skiing and so lower tolerance of ski boots and a technique which will cause more pain in boots.
I am not sure you can square all these.
I’d try going to a dry slope, or indoor snow slope for an introductory lesson package if she is new to skiing, or for an hour if she isn’t, and seeing if they can fix the problem with the rental boots they have, and they work on the slope as well as in the shop.
If they can – ? identical boots cheap off ebay? – or prebook identical ones in resort? – or ?? make the slope a lowball offer?
If budget isn’t an option, yes – a good fitter, here or in resort. Soutions 4 feet always considered the best, but I think Colin may be more about racing/performance fit.