Hi there!
Sounds like there could be a couple of different things going on.
First off -- you mention this:
She has never been the best at going down, lying down and has only once fallen asleep awake once.
-- is this generally how she's always been (though with 2-4 wakings) and she's just recently started waking up more?
We think he might have a bit of acid reflux happening. Maybe that's the case with her too and why she likes to be more upright?
This is a really good thought -- I'd have a read of this:
Reflux 101 - General reflux information and see if any of it rings a bell. Both teething and starting solids can trigger reflux flares so there could be something to that.
What does your daytime routine look like right now -- if you could put it in this form:
E -- when does she eat, how much, etc
A -- how long is she awake for, what times
S -- how long does she sleep
that will be a big help.
Generally, what do you do when she wakes?