When to go from 2 naps to 1

I am starting to wonder if DD is almost ready o just have 1 nap during the day. At the moment she has 1 nap around 10:30 ish for 1-2 hours and then another nap (which she is quite difficult to get down for ) about 3:30/4, then she goes to bed about 9ish. I am beginning to think that she is ready to have one nap around 11:30ish hopefully for a couple of hours and then to bed earlier.
I am finding it quite draining having her up so late because I never really get a chance to just sit and relax.
Previously when we have been putting her to bed earlier she doesnt sleep all the way through the night, she wakes up about 3ish and is difficult to get back down, but I am sure that is just something that after a couple of night she will get the picture that it is not get up time.
I guess my question is how do you get them to go longer between sleeps, and how do oyu make sure that they do sleep for long eough when they go down?
Do you think those signs are signs that she is ready to move to just one sleep?

I guess you have to look at how much sleep she is getting in a 24 hr period..???
My DD#2 stopped having her second sleep around 14 months....
She wakes at 730am. Has 1 x sleep at 1230pm - 230-3pm. Then in bed at 630pm.
Maybe you could stretch the morning sleep to 1130am like you suggested.....hopefully she will sleep at least 2-3 hrs....by 7pm at night she would be (hopefully) ready for bedtime.
I find 'wearing' them out in the morning helps...i.e i take my girls out in the backyard, Sophie runs around not doing much, but using loads of energy....it zonks her out by 1230pm. Whereas i find if we dont do much in the morning...i do housework, she follows me around the house, she takes a bit longer to fall asleep, and doesnt sleep for as long....
Anyway, i dont know if this helps.
I remember DD#1 changed her day sleeps around 12 months of age too....which is about where your DD is now.

don't know how much help this will be but my DD was the same at about 12 months. i would do everything i could to keep her up til 11 and then put her down i would keep her up in afternoon give her dinner at 4.30 bath approx 5 and bottle and bed around 5.30. she has got into this routines and most days has a 2-3 hour sleep in the day and goes to bed no prob at 5.30 and doesn't stir til 7.30am most days. Some people have thought keeping her up was a bit cruel but after a week or 2 she got used to it and now i don't have a prob she sleeps like and angel. Good luck

My first daughter Matilda went to 1 day sleep around 13 months. She was doing the same thing, sleeping well for the first sleep & then crap all for the second sleep & then would go to sleep late at night. When we cut out the second sleep she did really well and started having her day sleep around 11am (at first, it took us 3-4 months to move that one back until midday), and cut out the night sleep she started going to bed at 6.30pm which we loved.

I usually go to one nap when they start doing what your daughter is doing.. Although my boys were a little older.. I would 'try' keep her awake till 11 or 11:30 and put her down then.. or maybe go for a walk in the morning (if possible) so she has a small nap in the pram or something then a later sleep after lunch