:( for your DD, PDog. Maybe the longer naps are an age and mobility thing, as DS is doing it much more than he used to, and he's only a few weeks younger than your DD.
He's still looking tired today. He had a normal first nap and we had to wake him after 2 hours at the second, although it was later than usual. He didn't go to sleep till nearly 9pm tonight - late for him
The night was okay ta, IC - DS woke shortly after I got to bed (normal) and not too many times after that, although he was on my chest again at the end. I think I could manage to get him off my chest and back next to me if I waited till he was fast enough asleep, but I tend to drop off first.
fifitot, if I had your DS, I would try swaddling. Seriously. DS was swaddled till 5 or 5.5 months, and I only stopped because he suddenly decided he hated it. Before that, he really struggled to stay asleep due to the flailing arms. (I tried to wean him off it twice before, but he'd wake 8/9 times a night vs only once or twice when swaddled.)
You can get swaddle blankets for bigger babies - something like the Peke Moe or Woombie might do, and can be used as more of a sleeping bag once the flailing settles down. I know someone who still swaddled their toddler's arms for naps till he was almost 2 years, I think. He loved it!
Babies wake after 45 mins because it's the end of the first sleep cycle. That first cycle (and nap cycles) are usually 45 mins, whereas for the rest of the night, sleep cycles are usually 1.5 - 2 hours long. Sometimes waking after that first cycle is developmental - DS started it during the 4 month regression but it stopped again afterwards.
Sometimes it's to do with not being able to settle themselves between sleep cycles - which is why my DS has usually been waking then since about 6 months or so. I've found it to be the most predictable of all DS's wakings and the hardest to eradicate.
But I also found that settling him without a feed at that waking meant I was much more likely to be able to settle without a feed at future wakings. If I lurked and patted him as he stirred after 45 mins, there was even some chance he might not wake after the next cycle. Likewise, that's the time PUPD is most effective for me (I'm not prepared to try it at bedtime as it would involve him crying). Dunno if that's just one of his quirks or whether there's some biological reason for that waking having an effect on the rest of the night.
IC, I find that if DS is overtired he doesn't wake after 45 mins because he's so shattered - I know other people's DC are the same. So I'd guess that in your DD's case, it's the 9mSR to blame for it rather than overtiredness.
You could certainly have a go at shortening one of her naps - maybe the first one and see if it gives you better nights. You might need to bring her second nap (and bedtime) a bit earlier though. According to Helen Ball from the Sleep Lab in Durham, it's total sleep that matters (although according to the sleep books, not being awake for too long between naps is important too).
She does seem to need less total sleep than some babies, and I wonder whether getting more of that at night might mean she found it easier to stay asleep in a non-moving pram in the day? That's pure speculation though. 
If she did have more sleep at night & less in the day, at least you could rest a bit more rather than having to pound the streets.
I'm always too cautious with changes but actually I think it's fine to try something different for a few days and go back to the previous system if it doesn't help.
I'm wondering myself what to do about DS's tiredness - bedtime is creeping later but his naps are currently good. But he gets hysterical when woken from his second nap if he wants to sleep more - bf is the only thing which will calm him then, which is a bit :( if DH is looking after him.