I personally thinks it was definitely Rosa.
The thing is that Rosa is unable to actually control her emotions and always blame OTHERS instead herself or the right person.
Of course, there is nothing that can confirm if everything shown in Ep4 is 100% trustworthy, but if we start the premises of this, and how Rosa was shown "trigger happy" in all Episodes, it is very likely that Rosa was really unable to love Maria and blamed her for being unable to get happiness.
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