。
I had mother mend this sweater for me.
Literal
Mother [from-に] this sweater [obj-を] mended-for-me [received-もらった].
~てもらう is the complement of ~てくれる: instead of 'someone did X for me,' it's 'I received the favor of X (from someone).' The agent takes に (the source of the favor), and the speaker is the implicit subject. つくろう is an older, softer word for 'mend/repair' clothing (contrast with 直す, which is more general). Note つくろって here is the te-form of つくろう (繕う), not the volitional of つくる.