Hi, KB. I have some thoughts. First, I wouldn't necessarily jump to the conclusion of needing only 1 nap just yet. While it is entirely possible even at 11 mos, sometimes it's just a phase and she'll be back to napping more regularly soon. My suggestion would be to limit the morning nap to 1-1.25 hrs so that she will have enough A time before the second nap. It is natural for her to lengthen her A times, so since she will still need to nap, you want to leave enough time. Lengthening A times is how she will eventually come to consolidate her naps. However, if you strongly feel she is ready for one nap, I have been told to expect a period of time where the one nap will be only as long as she's used to napping (1.5-2 hrs) for awhile until her system adjusts. Therefore, you would need to compensate for less sleep with an earlier bedtime.
Has she reached any developmental milestones recently, or is she teething? Both of these can cause havoc on sleep. What do you do when she wakes at night; does she settle easily?
Have you checked in with the Birth Club Forums at the top of the EASY Forums? It would be a great place for you to "compare notes" with moms of babies your dd's age.