I would not suggest that you give the baby sleep aids, 6 hour time difference will be hard enough on a small baby, let along a druged baby. I would suggest two things, if possiable book her her own seat, I can imagine that it cost more, but well worth it, even for yourself, you get all that extra space... I love traveling with my kids, I get three times the room, and don't mind cuddling them at all. If this is too much to afford -you only get that free seat for another year, then I would suggest a few things....
1. Contact the airline right away, and request that you sit right behind first class, typically they have "baby" racks" that will act as a crib for newborns, not sure if this would hold her, but you get tons more leg room, and may be able to put her in an umbrella stroller depending if the stewardest are cool.... (Bring extra choclate bars and offer it to them...bribery works wonders when your traveling with kids) Seats next behind first class have more room.
2. Order a kids meal for yourself, even at one you will be suprised at all the great little snacks they give you in a kids meal, I've Trecked over 60,000 around the world with babies, toddlers and kids, and have experienced that the Kids Meals are by far the best tasting and value... all sort of snacks come with it to help keep her busy.
3. Shift work... forget drugging her, and enjoy that glass of wine they offer.... When we fly with 5 we typically pick 4 seats together and 1 away... may be in the same row, but away.... one of us takes the first "leg" with the kids, while the other rest and relaxes, it also helps us "notice" if our kids are behaving the way they should on a plane... When your leg with the baby is done, swich seats with hubby put in a movie sip the wine and set back... or catch some zzzz's till it's your shift again.
I would avoid her "late" nap if you are flying a bedtime.... I would suggest bringing her in the airport in her PJ's... get her something sweet and "play" with her, some airports internationally have play grounds inside (about time) and let her burn that engery off... she will have a major sugar crash (warning, don't over do the sugar thing or it could kick back on you... Hersery Mini's are perfect! for the kids and the stewardest)
and should rest most of the way... Since it is a night flight you shouldn't have to bring a lot of toys... she is old enough to learn that it's bedtime and that even if she doesn't sleep other people are, small play doo, crayons, and other bits that she can use with her fingers is perfect.... cherrios and string to make eatable necklaces will keep her busy, and then she can make some for her friends on the flight...
Ans last but not least... REMEMBER you are not the only person that have ever brought a baby on a plane... most of the time when thoses stressful moments do pop up she is not as loud as you think.... if someone offers to help you out on the plane take them up on it.... sometimes someone new can shed a new light... they're in this with you...
Good luck and enjoy your family... Warsaw is wonderful, can't wait to fly there myself!