More details would be helpful. You don't say whether she's fighting sleep while being jiggled/rocked/sung to, but if not, she may need physical assistance from the adults in her life to help her unwind and settle down, and those interactions may really help. If you're just putting her directly into her crib for naps, she may still be too involved in all the learning and interacting she's doing to let it all go.
Fussiness and sucking her hands could indicate teething or hunger. Four months is often a fast-growth period, and larger or more frequent feedings can make a difference in the baby's overall contentment. Does she use a pacifier? Have you tried feeding her a little more often?
If any video or television is involved, this can actually alter brainwave patterns in ways that indicate disturbance, too. There's sort of an entrancement that can happen with screen time that's very hard for little ones to let go of when it's then removed.
White noise during her naps may also help, and swaddling is great for many children, all the way up to a year or so.
Quite a few families I know with under-one babies have gotten great results from the tips in The Happiest Baby on the Block by Dr. Harvey Karp.