Just offering (((hugs))) - my DD has rarely slept anywhere but her cot since 4 months of age. To be honest I just plan my day around her naps, and if there's something unavoidable that will interfere with nap time, I try to just make my peace with the fact she'll get OT that day and get back on track the day after. Sleeping out and about is often difficult if you have a LO who sleeps well at home as they just aren't exhausted enough to do long naps when there's so much more interesting going on. The only babies I know that do good naps out and about are those that have awful nights! (Though I'm sure that's not true for every baby who sleeps well in the pushchair/car).
In theory you probably could use the same methods that you did to help her sleep in the cot to teach her to sleep in the pram - you could try something like a snooze shade to block out light and visual stimulation? It didn't work miracles for us but others swear by them.
As they get older and can stay awake longer it does get easier to get out and about - now we're mainly on one nap we do something in the morning, come back home for lunch and nap time,then can go out again in the afternoon.