、。
After she says it, Mayu-chan ends up ducking her head in embarrassment.
Literal
Say-[after-てから], Mayu-chan [topic-は] embarrassed-[looking-そうに] looks-down-[unintentionally-てしまう].
~てから gives strict temporal sequencing: 'after doing X, then Y.' ~そうに is the adverbial form of ~そうだ (apparent/likely), modifying the following verb: 'in an embarrassed-looking way.' 俯く (うつむく) 'to look down, to hang one's head,' often in contexts of shame or shyness. The closing ~てしまう gives the action a nuance of 'ended up doing so' — something she couldn't help. Combined, the sentence paints a single motion: saying something, then ducking her face because she can't help it.