Thanks for your replies!

I forgot to add in the earlier post that Du Tillot complained of Amalia's fondness for the guards and spending money on them so he had one regiment
replaced. I've also read that she played blind man's bluff with them. But didn't she also play with the beggars she allowed to live in the palace? So playing with the guards do not amount to outright affairs. Later on, she was also accused of having affairs with the grooms/stable boys, who were 'hunks'.

Well, Du Tillot's successor de Llano was also said to have 'entreated' her to end her 'immoral' lifestyle. I don't know where I read this, I think in Wikipedia much earlier. But how could de Llano do or say such a thing to her when both did not have confidence in each other? And he himself had a mistress. Amalia replied to Maria Theresa that she didn't want to give her confidence to anyone she did not know (and de Llano should be the first to earn her confidence, not her) and even alluded to de Llano's private life in stating her reasons for not trusting him (Maria Theresa demanded this).
At the forum I mentioned earlier (a French one), it was said that she tried to 'forget' her marriage with said affairs. A charge highly unlikely since we see her declaring in 1772 that she loved her husband very much (in spite of Ferdinand's infidelities). In the same forum, I've read that Maria Theresa in 1772 thought Amalia continued to
misbehave on 3 counts: 1) she continued to dominate her husband; 2) she continued to meddle in political affairs (despite her denials); and 3) there were entertainments at Sala Baganza (where she had her country house/hunting lodge) and at the palace in Colorno that Maria Theresa thought were unsuitable or inappropriate. We know the replies of Amalia to her mother's accusations based on replies #18 and 19 of this thread, when MT sent her that list of prescribed rules on her behavior through Count Rosenberg. But I don't think anyone can classify any of the accusations MT made against her as evil or 'mortal sins'.