They can subpeona your friend to come to attorney's office for a deposition, and ask that she bring bank records, phone records, credit card records, and the kitchen sink. She can attempt to have the subpeona quashed, but the judge will likely allow it if wife's attorney can show reasonable cause. What is reasonable is anybody's guess in Probate Court.
Once she gets to the deposition, they can ask her anything they want, and technically she can't refuse to answer it. I know because this happened to me personally. I wouldn't call it a scare tactic, I would call it harassment.
As my daddy used to say, however, "askin' 'aint gettin' ". It costs a lot of money to go through all those motions to shake your friend down. If there is nothing to hide then you have no worries. In my case, I showed up with no documentation whatsoever and told them I don't save such items. Sounds like your X's lawyer is wasting her money if he subpeonaed an account that never existed.
As for the reason WHY she would want to look for more of your money, um,
that seems sort of obvious. She wants more money! She's probably also jealous of your relationship with your friend and wants to shake her up. If she's really a good friend, she'll weather the storm with you. I did with mine, ten years ago, and he just called me two minutes ago to tell me how much he loves me. Hang in there, Peter.