If you buy a fully flexible open return then you're probably paying the equivalent of two one-way fares, it would be cheaper to buy the cheapest return ticket and throw the other half away and buy a fresh cheap return ticket should her return date change.
To/from MAN to Kiev the likes of KLM and Lufthansa operate, go online to KLM and/or Lufthansa websites and go thru the motions of a cheap booking, selecting a return date of her maximum length of stay, let's say 3 or 6 months, this is just a dummy booking for you to establish the ticket rules, often the return date of a cheap (ish) ticket can be changed for perhaps a EUR50 fee subject to seats of the same booking class being available on the flights you want to change on to.