Can I claim a modification I made to my vehicle for my disabled daughter in the state of oklahoma?

[JulieR]

Yes. The cost for modifications to the van, to make it wheelchair accessible, is a medical expense which would be deductible on Schedule A of your return, if you itemize your deductions.  You can include in medical expenses the difference between the cost of a regular car and a car specially designed to hold a wheelchair. 

See IRS Publication 502 page 7 - https://www.irs.gov/pub/irs-pdf/p502.pdf#page=7