。
It looks like she's hiding something to surprise me with.
Literal
She [topic-は] me [to-に] surprise-cause-do thing [object-を] hiding-is [seems-ようだ].
Two productive grammar patterns stack here. (1) びっくりさせる ('surprise [someone]') is the causative of びっくりする ('to be surprised') — 'cause [someone] to be surprised.' びっくり is itself a 擬態語 (state mimetic) for sudden shock. (2) ~ているようだ adds the evidential frame: ~ている marks an ongoing state ('is hiding'), and ~ようだ marks the speaker's inference based on observation ('it appears that'). The subordinate clause [私にびっくりさせる] modifies もの — 'something to surprise me with' — using a relative clause. The whole sentence reads as careful, considered observation.