Before a nap/bedtime I offer my ds water so that I know he isn't going to be thirsty. Can you feed say 1 hour before without her falling asleep, so you know she is ok.... feed her if she starts drifting, take her off & go & do an activity. that way you can be confident thirst isn't part of the issue.
To be honest it could take 2 hours & occasionally longer... for me the longest was just over an hour, but usually it peaks around 10-15mins & then cycles, repeating, gradually they loose steam.... so in all honesty 10mins is actually not that long. As long as you stay with her comforting with soothing words & You remain calm, she will learn. After about 30-40 mins it is good to step out of the room & give you all a break, you could offer a small snack & drink from a sippy at this time too. Then go back & start, It is also a really good idea to have a "routine" you do before trying to settle her, so she knows what is happening next. I change nappy, then we sit & read a couple of stories & then I cuddle him & sing a quick song & then into the cot... that way ds, knows it is nap/bedtime, because it is the same routine every time... if you leave the room, start your routine all over again. Also have a verbal message you keep repeating. for me it is "it's ok, nighty night". What you want to do is change what she sees as the "cue" for bedtime/naptime.
As you have always stopped at about 10mins, that will be the hard part to get through, so it might early on be a point at which you go back & repeat the "settling routine" to "help you" get past it