Crypto Tax

By default, any income worldwide is taxable in Germany while you reside here - this is true for crypto gains as well as all other sources. She will have to include any realised gains in the tax declaration next year.
Many countries have tax treaties with Germany that in some cases (but not all!) prevent double taxation. If a treaty exists with your country and it gives your country the right to tax such gains, they are not taxable in Germany. But you still have to declare them, because the tax authority (not you) decides what is taxable and what not. (Not declaring is a criminal offence and can get you into more trouble than it's worth!)
Engage a tax consultant to do all this right!

Just for completeness sake: There is also a gift tax for presents to others (up to 50% of the gift is due as tax!), but the tax-exempted amount for married couples is € 500 000 within 10 years, so hopefully that will apply to you. (If you are not legally married, the exempted amount is far lower.)

On your question, In the case of a disposal transaction in Germany that took place during the year of ownership, there is an income limit of up to €600 per year within which no tax is levied. However, this limit applies to all private transactions made during the year in question, i.e. not only to the taxpayer's Bitcoin transactions. The taxation of the taxable capital gain is calculated as the difference between the sale price and the purchase price plus the advertising costs for the Bitcoins in question (e.g. the purchase price of the previously acquired Bitcoins or the costs of finding them).
Perhaps it is best to exchange the cryptocurrency with each other, you can do that on this site for example: changelly.com/de/exchange/btc/usdt .