Legal Question in Family Law in Colorado

Unfortunately, there is not enough information here to really answer your question. Strictly speaking, for as long as there are any financial related orders (child support, spousal support) between you, there is the possibility of her continuing to demand more. So we're potentially talking about until your youngest child no longer is entitled to child support, or until the period of maintenance expires. How much she can do successfully depends on your Order and what she is asking for. There may be some defenses.

Usually, expenses that require agreement and can be billed are related to activities for children, so I will answer your question in that context. If she's claiming you agreed but you did not, then try to make sure there is always written communication about these things. If she talks to you, be clear when you're talking to her and then send her a text or an email confirming the conversation. Keep it civil and to the point. Something like "Today you asked me about putting our child in gymnastics. I explained to you that I cannot agree because I cannot afford another activity right now. If you want to cover the cost on your own, I don't object to the activity itself. I do not agree to this activity though." Don't get sidetracked into blame or accusations. Then if she tries to have the Court make you pay it, you have something to show that you did not agree. Also DO NOT just say "I don't care." That is not a clear expression that you do not agree, and looks more like agreement than disagreement.

Documentation can be the key on things that require agreement/approval. Keep it in writing, and keep copies of the writing. If it wasn't agreed to, and your Orders say you only have to pay it if you agreed, then you don't have to pay it. If the other parenting takes you to Court to make you pay it, you will need your documentation showing that you did not agree and that you expressed it clearly will be your defense. If you can prove to the Judge that you didn't agree, then you will not have to pay it.