Someone wired my friend money to supposedly help pay a bill now that the bill has been paid they are demanding her to pay it back and send it to Nigeria they are saying she stole the money and is going to press charges. Can they do that? She is a single mother and she’s freaking out that the cops are gonna show up at her house. Every number they contact her from is a google voice number. Should she be worried that they are going to call the cops?
UPDATE: After comments from Hart CO, I've removed references to "wire-transfer" as these mostly can't be reversed (see this question on Quora), although they can be in some cases of fraud (e.g. perhaps if the scammers sent a wire-transfer from some other victim's hijacked account).
If the OP's phrase "Someone wired my friend money" does actually indicate a wire-transfer was used to send the money, then the chances of it being reversed may not be as high as my original answer indicated (and the scammers are relying on the bullying-power of threatening to press charges to get the OP's friend to send them "untainted" money2). If that phrase was used more generically to indicate money was sent somehow to the OP's friend, then there's still a good chance it will be reversed).
In either case, the situation is still almost certainly one of scammers targeting the friend, so she should still contact her bank and possibly the authorities.
It is almost guaranteed that they are not going to call the police, however it is also almost guaranteed that they are trying to scam her and that the money they sent is likely to disappear soon. There are many similar stories on PF&M, including Can I be arrested for not returning money someone else deposited in my bank account? which includes the threat to involve the forces of law and order.
The basic premise of scams like this is that money is sent to a victim through a process that is reversible (cheque, direct bank deposit etc.) and then "extracted" from the victim through a non-reversible process (MoneyGram, Western Union etc.). Often, the "extraction" is done by playing on the victim's greed (getting them to send some of the money on to other people the scammer names, but being allowed to keep a large part for themselves). Latterly, as here and in the linked question, the extraction is done through threat of legal trouble. In either case, (ideally after at least some of the money has been extracted) it will be found that the original deposit/transfer was in some way fraudulent, and will be reversed. If the money has already gone (either to pay a bill as here, and/or by sending via MoneyGram), then this may leave the victim overdrawn and with a new set of problems.
Your friend should probably speak to her bank as soon as possible: depending on exactly how the money originally arrived, where in the world she is, and what information she may have given the scammers, there is a chance that the scammers may be able to do other things with her account. Once told, the bank should be able to monitor or block any such activity. Also, while the bank almost certainly can't stop the money being reclaimed1, if that is going to leave her in a difficult financial position, they may be more sympathetic to her if they know the situation.
1 Note: this isn't a case of the system protecting the scammers. The money she received was almost certainly not the scammers' money. Either the payment was completely faked (e.g. a bogus cheque) or the money was sent from the account of an earlier victim. In either case, the money – if it actually exists – doesn't belong to your friend.
2 If the scammers did send a wire-transfer from a hijacked account, they could, of course, have sent it directly to one of their accounts. However, involving the OP's friend, even it only works if they can bully her into forwarding the money, leaves an extra "jump" if the banks try to trace exactly where the money has gone (an a successfully-bullied person is less likely to involve the authorities). And, if it doesn't work, the money was not theirs (the scammer's) anyway, so they've never actually lost.