The only advice she got from the travel agency is to use disability services.

Not disability services, but you can use the meet and assist services from the airline that are provided to minors. The same service is available for elderly travelers and those needing extra assistance. This would make sure someone receives her at the gate, takes her through the terminal, and places her at the priority queue for the next flight.

The other thing you can do for her is minimize her transit points. Try to find a route that has at max one stop. You didn't mention where in Europe you would be starting from, but I would recommend Emirates; not only do they have a large multi-lingual cabin staff (they also make sure that there is staff speaking the destination language on their long distance flights) but she would be transiting through Terminal 3 (dedicated to Emirates) its very little chance to get lost at that terminal.

Some other things to consider is the stay at the transit point. For example, try to get her a meal voucher in case she needs to snack at the terminal (these are available from the airlines).

At most terminals they can charge you in the local currency or a major currency; also if you pay in cash (very rare, but happens) they will reimburse you in the local currency.

All this can be daunting for someone that has a language barrier.

The only advice she got from the travel agency is to use disability services.

Not disability services, but you can use the meet and assist services from the airline that are provided to minors. The same service is available for elderly travelers and those needing extra assistance. This would make sure someone receives her at the gate, takes her through the terminal, and places her at the priority queue for the next flight.

The other thing you can do for her is minimize her transit points. Try to find a route that has at max one stop. You didn't mention where in Europe you would be starting from, but I would recommend Emirates; not only do they have a large multi-lingual cabin staff (they also make sure that there is staff speaking the destination language on their long distance flights) and as she would be transiting through Terminal 3 (dedicated to Emirates) it reduces the chance of getting lost at that terminal.

Some other things to consider is the stay at the transit point. For example, try to get her a meal voucher in case she needs to snack at the terminal (these are available from the airlines).

At most shops they can charge you in the local currency or a major currency; also if you pay in cash (very rare, but happens) they will reimburse you in the local currency.

All this can be daunting for someone that has a language barrier.