I have noticed something like that too. It seems that only for starting the bid you must have the money. Lets say you have 100M. You can bid for two players worth 70 millions each. If you won both bids, your team's budget will be -40M. Same thing that might have happen with this player. When she made his first bid, she had the money, but then the budget became negative when she won some other players.
This is one of the flaws of this game which can be exploited.
Someone please confirm this.