The main tax liability would be due in Ireland, where you are a tax resident and receiving the gift.
If my understanding of the situation is correct, you should not be liable to any tax in Ireland. You are receiving €100k, when the current CAT gift/inheritance threshold from parents is €310k. If you receive a further gift/inheritance, you will have to pay CAT on anything above the applicable threshold at the time and the €100k you receive now will count towards is. If you are expecting a big inheritance, it might be worth seeing what other solutions there are.
I cannot see what tax liability your mother would face in Germany for gifting you €100k. From a quick google, if you were resident in Germany, you would also be under the applicable threshold (€400k).
I imagine Revenue could ask for justification on the source of the money.
That is a simple assessment. A professional might have a more tax savvy solution depending on the situation and objective?