you could try to nest the tickets, as the inner one is only a month appart.

Also for the european part there may be more than enough lcc.

perhaps there is one airline where two one ways work that far appart

I tried ita but it does get timed out with that request

It may actually be cheaper to buy miles and get your girlfriend those two one way flights at the end of it and use a nested flight in the middle.

Get on the phone with your favorite airline and let them do some searching - i find that most call center lines are actually helpful and the more complicated your problem is the more worth is the invested time in them.