If you've got upto 7am wake up times I would start waking her at 7am then do nap at 12.30/1pm whichever A time you think suits her best then work on 1.5hr nap and bedtime 5hrs was it after that then just stick with it. That way if you control her wake up time you can set nap at set time but it will also be the A time she needs and if you keep nap to set length you can then fix bedtime to be required A time post nap. does that make sense?
You know how long she will sleep at night, right? you also know what A times she needs pre and post nap, whats left in the middle is the length nap she can take to keep to these timings.
As you know Lily never took a long nap because she does 12hr nights, when her nap started extending and I let it she started waking early in the morning, so I've fixed it back to set nap time and length & bedtime, it works for us and you can plan your day around it.
does that help honey?