Bis zu ihrem Abschluss in Psychologie möchte Andrea nicht umziehen.
Why ihrem after akkusative bis?
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The preposition "bis" can be used with the german Akkusativ and Dativ as well. Usually "bis" with Akkusativ but if you use "bis zu" then the Dativ may follow (Temporal preposition).
Usually one can omit the "zu" when using "bis zu" and it seems "bis" would required always Dativ which is not true. You can find and construct a variety of sentences using either of the casi.
Best wishes, SG