Hi @trialdoggy,
Based on your mention of the US SSI, I’m assuming you both are U.S. citizens.
The first question from my side is what type of residency permit your daughter would receive. In my view, she would only be potentially entitled to a permit according to paragraph 36 of the residency law. This covers family members who are not minor children or spouses. They can receive a permit in order to prevent ‘extraordinary hardship’. If your daughter has a disability which requires you to care for her, then this could be considered such a hardship. The immigration authorities would likely want to know about her current care arrangements, guardianship status and whether there are other potential carers in the U.S.
Here is an article by a lawyer’s office (translated online from German) which goes into details about such cases:
https://buemlein-***.translate.goog/auslaenderrecht/nachzug-sonstiger-angehoerigen-eltern-pflegekinder-sonstiger-verwandte/?_x_tr_sl=de&_x_tr_tl=en&_x_tr_hl=en&_x_tr_pto=wapp
An important requirement for this permit is that you have sufficient income to cover the living costs of both of you, including statutory German health insurance. The SSI benefit can be taken into account when assessing if you have sufficient income.
As U.S. citizens, you may both travel to Germany without a visa and apply for a residency permit here. There is no requirement about the German language.
Let us know if you have any further questions.
Best,
Éanna