Aww don't feel inadequate.
If it is taking hours to get her to sleep, I assume after at least some time happy/awake - then it really does sound like the over-arching problem is too much awake time between naps. Good sleep promotes better sleep and sadly poor sleep just leads to even worse sleep get into a horrible spiral of over-tiredness leading to poor quality sleep leading to more over tired more poor quality sleep and so on.
The great news is though that babes often get into this downward spiral and that is solvable, you can and will get through this. It wont be like this forever 
For now, focus on "Project Baby Sleep". Clear your diary of any must-dos this week. Accept that little/no housework will be done. That you might eat crap rather than spending time preparing meals and that you may spend the vast majority of the week sat on the sofa or lying in bed and make peace with doing that.
Your entire focus wants to be on getting this baby to sleep often. Don't clock watch how long she sleeps for, clock watch how long she is awake for. If it takes ages to get baby to sleep then you might have baby waking, being fed and then immediately working on getting her back to sleep. So that hopefully after an hour of trying she eventually does drop to sleep.
Do everything and anything that works. If pushchair walks work, push chair walk a lot. Have you tried swaddling her in the pram? Co-sleeping and swaddle on your bed for naps?
No sleep method is necessarily mean you put a sleepy baby down and they quietly go to sleep. If only! That's the stuff of naïve rose-tinted expectations when pregnant, not a reality.
So if you use a bouncy chair example, you may need to keep on bounce, bounce, bounce, bouncing. Putting dummy in. Bouncing more, dummy back in, bounce, bounce, bounce and so on and so on. Eventually. Eventually you get there. Then you sit back and breath a massive sigh... and then baby wakes up and it starts all over again!
Same with pushchair rocking. Same with a baby sling or whatever you use to jiggle baby to sleep. You just have to keep on going.
Good luck. It'll be fine [tea]