>her given name
The kanji of Youmu 妖夢(ようむ) mean something along the line of "bewitching dream".
It's also a shortening of the title of the game she first appears in: 東方妖々夢~ Perfect Cherry Blossom.
The same characters also appear in her stage theme 東方妖々夢 ~ Ancient Temple.
For those who don't know: 々is the repetition character for kanji: 妖々夢 = 妖妖夢 = ようようむ = youyoumu
One could say that her character as well as her stage represent the essence of the game she appears in.
Further, in the afterword of the Perfect Cherry Blossom's demo it is stated that the 妖々(youyou) from the game's title comes from Sei Shōnagon's The Pillow Book, a book completed in 1002 written in Middle Japanese. More specifically, the name as well as the game's setting are based on the following line:
「春はあけぼの。やうやう白くなりゆく山際、少し明かりて、紫だちたる雲の細くたなびきたる。」
"In spring it is the dawn that is most beautiful. As the light creeps over the hills, their outlines are dyed a faint red and wisps of purplish cloud trail over them."
So, 妖々(youyou) comes from Middle Japanese やうやう(yauyau), which meant "gradually", cf. Modern Japanese 漸う(youyou) "gradually" and 漸(yaya) "somewhat".
妖(you) was read as "eu" during Middle Japanese times, so the kanji usage only makes sense from a modern perspective.
Unfortunately, ZUN doesn't explaing where the 夢(mu) comes from. "gradually dreaming" doesn't make much sense.
In short, the kanji of "Youmu" mean "bewitching dream", but the meaning of the you-part is actually "gradually".
In that, her name is similar to other Touhou names like "Marisa", where the meanings of the reading and writing of the name don't align.
>her surname
Konpaku(魂魄) means "soul" in Japanese.
魂(kon) is the "soul of the body" and goes back to the Earth after death.
魄(haku) is the "soul of the mind" and is judged by the Yama upon death.
Normally, both souls reside within the body, but in Youmu's case her soul of the mind her phantom half following her around. In fact, ZUN also calls it a hitodama.
>do you think it fits her
Absolutely.
The Kanji of her given name probably represent the essence of spring as explained by Sei Shōnagon and pertain both to her environment's setting like the bewitching ghost cherry blossoms of the Netherworld and to the essence of her own species.
The name's reading is, of course, a homage to the Pillow Book, but "gradually" also shows diligence and persistence. After all, the player has to beat her thrice in a row in Perfect Cherry Blossom.
Her surname perfectly describes the concept of her own species with divided souls.