What does "no me ha gustado mucho unos regalos que me ha comprado mi hermana" mean?

The presents that your sister has bought for you.

The end part of the sentence is talking about presents that the speaker's sister has bought for the speaker. If it were the other way around (talking about presents the speaker has bought for his/her sister), the verb would be "he comprado" (I have bought) rather than "ha comprado" (s/he has bought").

I agree with Esther below (and shouldn't have gotten a thumbs-down). A bit freer translation (without insisting in translating literally "ha gustado" (should have been "han gustado") and "ha comprado") would be: "I didn't like some of the presents my sister bought me very much". Could even have been a native Spanish speaker...just with a "imperfect grammatical" sentence. There's all kinds and levels of Spanish.

Some of the gifts that my sister has bought for me, I haven't liked very much. You can tell because it says "que me HA comprado mi hermana". If it meant the gifts that you had bought for your sister, it would have been "que le HE comprado a mi hermana", which wouldn't make sense. Why would you give your sister presents that you didn't like very much? The conjugation is much more important than the word order.

It means: "I didn't like that much some of the presents my sister bought me."

I think it's something like 'I don't the presents my sister has bought me' but Im not sure.

Means : I liked some gifts that I bought my sister