If the OP's daughter is under the age of 12, then:

1) she cannot be booked without an accompanying adult
2) she would be denied boarding if a booking has been made without declaring her true age

If she is 12 or older, but still needs assistance, then:

3) perhaps it would not be a good idea for her to travel on her own, particularly when it involves a connection?
4) pretending to suffer from something when she does not, is probably not a good idea - it could have unintended consequences

Assuming she is not under the age of 12, how does she feel about the whole thing? Perhaps she should have a say. I know I would have been happy to do it (including international transfers) aged 12 and I would not have been at all impressed if my parents decided to 'fabricate' an injury to get me assistance.

Have you also thought about the potential issues of misconnect? If she's stuck overnight somewhere, can she fend for herself?

In addition certain countries may require additional documentation for a minor to travel, so you might like to check all the requirements properly and ensure that she does not suffer any unnecessary/unintended consequences.

I guess the best thing to do if you (or she) have concerns is not to get her to travel on her own. You'd probably know if she seems confident enough to deal with whatever travel may throw at her.