Ive got a few questions and a few suggestions:
1) How tall is she?
2) What sorts of things does she like?
3) What sorts of things does she not like?
4) Is she sensitive to things like noise or movement?
5) Does she have good sitting balance?
6) Can she walk enough to get into ride cars that require a transfer? If not, is she small enough to lift in?
For the tiredness, I have three suggestions:
1) You can get a sticker for her stroller that will allow it to be used in lines up to the point of boarding. This is called Stroller as wheelchair. Strollers are not normally allowed in most lines, but with this sticker, you can keep it with you and it will treated just like a wheelchair.
Certain attractions have a wheelchair accessible ride car - you wont be able to use the stroller in most of those because the stroller will be too low or not the right shape. You will be able to bring the stroller into shows and park it with the wheelchairs - for those, you will probably need to take her out and sit her on your lap, but at least you will have the stroller in lines so she wont get too tired and you wont have to carry her. You can find more information in post 6 of the disABILITIES FAQs thread, which is near the top of this board - or you can follow the link in my signature.
2) A good touring plan will help you with being in the least busy park and the least busy attractions in that park. Several touring plans people suggest often are touringplans.com and easywdw.com
Even if you dont use a full touring plan, just having the information about which park is likely to be most busy will be helpful to you.
There are also apps for smart phones that will help you to plan - they have estimates of wait times, to help you avoid the busiest places. If you have Verizon phones, Disney & Verizon have teamed up for an app called Mobile Magic, which has the official posted wait times for attractions and information on which attractions have Fastpasses available.
3) If she needs a rest, you can go to First Aid in any park. They have cots in individual rooms or cubicles. It is quiet and cool there. There is also a Baby Center in each park (not just for babies - small children too).