Is borrowing from a girl via transfers to support a business venture considered a forbidden act and an unlawful trade?

There is no blame upon you for the aforementioned work. The fact that you borrowed the amount from a foreign girl does not affect it. However, the relationship with her must be governed by Islamic guidelines, either by proposing to her and marrying her, or by severing the relationship. This is because Islam does not approve of romantic relationships and friendships between the sexes outside the confines of marriage, due to the potential harms they may lead to. You must repay the loan amount to her unless she absolves you of it.