She wrote to Stalin personally to give her a tank for that money, which he obliged.

“My husband was killed in action defending the motherland. I want revenge on the fascist dogs for his death and for the death of Soviet people tortured by the fascist barbarians. For this purpose I’ve deposited all my personal savings – 50,000 rubles – to the National Bank in order to build a tank. I kindly ask to name the tank ‘Fighting Girlfriend’ and to send me to the frontline as a driver of said tank.”

IIRC it was largely symbolic because what she had didn't come close to paying for a T-34, but they were willing to let her sign up regardless.