Depending on if your daughter has any income, you might be able to claim an Infirm Dependant amount:
http://www.cra-arc.gc.ca/tx/ndvdls/tpcs/ncm-tx/rtrn/cmpltng/ddctns/lns300-350/306/menu-eng.html
Also if your daughter has the Disability Tax Credit on file with CRA then, again depending on her income, she may be able to transfer a portion of the disability tax credit to you (providing she does not need all of it to reduce her taxable income).
http://www.cra-arc.gc.ca/tx/ndvdls/tpcs/ncm-tx/rtrn/cmpltng/ddctns/lns300-350/318-eng.html
You say the child support payments are not legally required...if such is the case, and it's just money you are sending to your daughter or to your ex, then you might be able to claim either or both of the above amounts, providing that your ex hasn't made a claim for credits for your daughter. If your wife makes any claim for credits for your daughter, then you will not be able to make any claims yourself. If the child support payments are due to a written agreement or a court order, then you are not able to claim any personal amounts in regards to your daughter.
