My son has done the stand up thing ever since he learned how to stand. At 14 months, your daughter can figure out how to lay down by herself. I'm not sure what soothing method you use, but continue with whatever worked for you before. Just do your normal routine and leave the room with her standing up. She'll get it. If you can't stand her crying, try doing the Ferber method and going in to soothe her quietly and quickly at specific intervals (5, 10, 15, 20 minutes), picking her up after an hour if she still hasn't fallen asleep. It takes longer for them to catch on to this method than just CIO, but it's better for your nerves and gives you a chance to check to make sure she doesn't need something else like a diaper change or water.
Also, is she still taking two naps? My son is almost 15 months old and I've been trying my darndest to keep him on two naps, but I just recently gave in since he was doing poorly with two short naps (if I could get him to sleep in the morning at all) and started transitioning to one nap instead. At first, he could stay up for about four hours before pooping and only taking an hour or so. If I tried again in the late afternoon, he wouldn't sleep, so if he wakes up from his nap early, I just put him down earlier in the evening (even if he fights it). It's been about two weeks (some days were two nap days during that time) and now he's more adjusted and can stay awake about 5 hours, goes right down for his nap, and sometimes takes two + hour naps in the afternoon. He still seems tired a lot because he was sleeping less during the initial transition, but his disposition has been so much better with one longer nap than two shorter ones.
Just watch your daughter. She'll tell you when it's time to transition (assuming you haven't done so already). My friend's daughter is two and is still taking two naps (but she goes to bed late and only sleeps about 10 hours at night whereas my son usually does 12 hours so she probably needs more napping time). Good luck!