Ur tc seems like its a US salary. And if ur sister is also in US, why move to Berlin? 49 seems low. But i know nothing about europe.
It's ok. Something you'd expect from non tech 2yoe
Life is cheap there, if she likes partying she’ll love Berlin
54k is average in berlin gross, so 49k is below average. “her to live alone and well?” Probably not if she is used to consumptive US life-style
Better to look for a baseline. Rent:Pay, mortgage-payments:pay, and property-prices:pay are good indicators of income bracket.