Compra is the third-person singular present tense of comprare (to buy). It matches la donna:
So la donna compra = the woman buys.
Adjectives in Italian must agree with the noun in gender and number.
Fiori is masculine plural, so the adjective must also be masculine plural:
Yes. Italian word order is fairly flexible, although the original sentence is natural and clear. For example, you could also say:
The original version sounds neutral and straightforward.