Hi there! Sorry you're having such a hard time of it, it's exhausting isn't it!?
I can't say I'm an expert, as I'm on here because of issues with my own 9mo. But I've had two sleep resisting cap napping daughters so thought my experience might help.
I see the problems started at 12 weeks. From what I've read, babies change at that age and no longer sleep like newborns (falling into a deep sleep quickly), but start to sleep like adults (falling into a light sleep first, with a sleep cycle lasting 30-45 min). I guess that's what happened here and your baby can't link sleep cycles easily during the day when the pressure to sleep is lower. This goes on until 6 months or later when babies become developmentally able to link sleep cycles (I'm still waiting with my 9mo).
My two babies were the same and only slept for 30min during the day. But, the crucial difference was that I was putting them down for 5 or 6 naps a day!!!! I think your baby is super overtired if she is only having 2 short naps. If she's sleeping for 45 min, I would aim to get her to have 4-5 naps a day. I know what you're thinking - nobody has time for that! But I expect it's taking her so long to fall asleep as she's chronically overtired. Until naps start to lengthen, try to get her to sleep in the quickest way possible - bouncer, buggy or sling. If it takes forever to put her down in the cot, try a different approach. With DD1 I took her out for walks, all day long! With DD2 that was more difficult as I then had a toddler as well, so I used the sling. But crucial is frequent naps! It's no fun having an overtired and grumpy baby.
I think starting the first nap sequence after 1.5 hours is far too late. Try 45 min after her morning wake up time. The first nap should always be after a shorter awake time for others. Tgen aim to start getting her to sleep after 1 hour awake time for every subsequent nap. Don't look for sleepy signs - by the time she's rubbing her eyes it's too late. Look at the clock instead.
I hope this helps! Sorry if I sound a bit brusque but I'm typing quickly as my 9mo is bound to wake up any second!
Good luck!