If she can prove your friends are paying you then you can be in trouble. Proof would be either by statement of your friends or by monthly bank transfer / deposits from them.
Gifts to help out are allowed and not necessarily considered rent. Besides, you couldn't be renting the place without a contract, etc etc... Just make sure you get the payments in cash and your friends won't tell her they paid and how much. It is a risky situation if she opens a complaint... illegal rent ouch.. :-)
Now for the best part:
What happens when she does not pay her share?
This might entitle you to 100% of the property and any other goods included in the settlement and your ex losing all her rights for not keeping up with her obligations towards the debts.
You'll get the right to take 100% of the assets and debts but if you don't want it she'll have eventually to pay her share, to you. Unfortunately because it is joint you have to pay her share if she fails and then the court will settle that she has to pay you her part.
I hope this helped clear your mind. I would meet her face to face, at the place and have her meet the people who are staying then have a friendly discussion with everyone together about payments. I guess friends would be willing to help and she'd be willing to accept if is can be deducted from her share? :-)
Regards!