Regarding lalena/lalona/laluna/lalíina/lalehena (generosity):
Please note the second generation developing Láadan has modified the "no reason" aspect of the first declension to "-íina" to disambiguate from "-ina" in the second declension. I've made the modification in the above restatement of your proposal.
The emotion expressed in English as "generosity" is meet, imo, for treatment in the first declension in Láadan. And I really like the inclusion of "lal" (milk) as its core. My only cautionary note here is that we already have "lena/lona/luna/líina/lehena" (trust) and its offshoot "lolena/lolona/loluna/lolíina/lolehena" [lo- (internal) + lena, et al. (trust)] (confidence). Do "lalena" et al. naturally join that semantic subdomain, or would another root serve better? Maybe "banena/banona/banuna/baníina/banehena" with "ban" (to give) at its core? Not counterproposing; just spinning thoughts. If consensus arises around lalena, et al., I certainly would not balk.
Regarding "dáanin" (grammar) [dáan (word) + yáanin (tree)].
My only quibble--and this is a general quibble, not one directed at you or this word in particular--is the elision of the initial /y/ from yáanin. While this is not Láadan best practice, there are many tree-adjacent forms in Láadan wherein the /y/ is elided, so I cannot in good faith bar this one.
It nicely fits in the semantic domain based in dan/dáan (language/word) including "déeladáan" (sentence) [déela (garden) + dáan (word)].
I'll just swallow my discomfort with the elision and support this proposal.
Regarding "óoyahowa" (inner power/energy) [óoya (heart) + owa (fire)]:
This is a lovely formation. I wholeheartedly support!
Small Piece or Fragment - híthi - I began it with hí for híya, followed by th- referencing then (break), with i as a diminutive ending. For fragment, which has a broken, jagged, negative feeling to me, something regretable: híthilh
Regarding híthi (small piece/fragment):
I have strong reservations about this formation both on morphological and semantic grounds.
Semantically first. This formation differs from "íthi" (be high/be tall) only by the initial /h/. Granted the semantic domains of "piece/fragment" and "high/tall" are sufficiently distant that, even when nominalized, "íthi" (height/tallness) would likely not be confused with "fragment." However, do we really want to create near-homonyms when we don't need to?
Morphologically next. Láadan does not have the drive to short forms that English does. Láadan does, however, always strive for morphological transparency. Keeping only "hí" from "híya" and only "th" from "then" and adding a legacy suffix that meant "affectionate diminutive" is problematic from that standpoint.
If I might offer an alternative: hiwud [hi- (diminutive) + wud (part)]. The prefix "hi-" doesn't just denote smaller; it connotes a lower-order version, so it fits well here. Of course, any word can be made pejorative by adding "lh-" or "-lh": lhehiwud or hiwudelh, though I think I prefer the latter to separate the too-similar syllables "lhe" and "hi".